Basic Classes in Terms of Difficulty?

Well, no, not for practical purposes.
For example you kit yourself out with with a BW.X with HVB.V your weight/power recharge bonus will be around -10%.
At -10% CB has 4.35s cooldown and TC has a listed 6.9s, but, if you do as described above, cloak-CB-shoot, TC has only ~3s cooldown (2.82s is the theoretical minimum), much shorter than a naked CB.

That's how it supposed to be at the start,
practice,
quick scoping (first aim without scoping, then scope and adjust)
and right hand advantage (you shoot by corners while you still mostly in cover)
will get you there.

That is this HFI's TC cooldown at 200% power bonus, here.

I know, cloak cooldown is a bit delayed, etc. etc., as said, theoretic minimum.

I was fine with everything you said until the bit I emboldened, as it made me wonder if you actually watched the video? It's only the intro that is from the Citadel - the rest is xcal outscoring a Destroyer Typhoon and a Reegar AIU without firing his gun. I'd say that's both fun and effective - and in all honesty in this instance not due to xcal being exceptionally skilled.

But I wasn't in any way trying to make it look like I thought you were wrong in not detonating TA, just alerting you to the fact that it's perfectly viable to use it offensively. The numbers don't matter as much as the timing, and the fact that it staggers (and/or finishes off) multiple enemies. I've done literally thousands of waves with the TSent, and the majority of them were with the standard tried and tested 46664 build, mostly with Arc Pistol, Phaeston, Saber or Lancer. In that time I've completed Overload Mastery 51 times, and Tech Armour 17, without ever actually speccing for an offensive TA build. So that's what I did last night, just for lols, after watching that video for the umpteenth time. Unusual approach, I admit - 55466 (full melee) with Wraith + Smart Choke, Omniblade and Strength Enhancer with AP ammo. By funny coincidence I landed in a GiP on Giant Hazard, though I had Reapers as opponents rather than Cerberus. I'm not a score-focused player at all but I came close to breaking the screen with the number of medals I had at the end -  you have to trust me on this - it wasn't just fun. 

Then how being the leader is advantageous? If I've asked already and my ditzy brain did not retain the answer, I apologize, it's a part of my charm. Does the raid lead get extra agro?

Cool, thanks, now I know!

(Waves) So far I am liking the Sentinel kit better than the Adept's. In Bronze at least, the tech armor x-plosion does pack a bit of a punch taking off the mooks that tend to sneak up on me. When passive, the armor makes the char a bit sturdier.

Not sure if I am doing the Warp right, but I go with throw first, warp after sequence. My liking for a Sent might have a bit to do with the pistol I actually have to give the character, that works surprisingly well. I am not sure how I got it, but it is an Eagle I from the 4th tier of weapons, and in addition by some reason I went from 6/13 uncommon mods to 10/13 uncommon mods.

So, I am a proud owner of Sentinel on level 16, with two promoted classes (Engi and Adept). And, well, Infiltrator is the next to try after I get my Sentinel to level 20. I am going to back-read the thread to put an Action Plan together for the Infiltrator.

Yep.

To really maximize your output, use Warp on armoured or shielded enemies, then shoot them. The gun will do bonus damage to the warped target, and when your cooldown ends and you use Throw, you'll get the combo described above.

For unshielded targets, you can just use throw. With the 30% bonus in Tech Armour, Throw actually receives a Force Bonus (which usually does not apply to Power Bonus Damage.) A more advanced tactic is to use Incendiary (or another priming ammo, but Incendiary is regarded as the most effective for combos) by shooting the target, then following up with Throw to get the Fire Explosion combo damage in addition to the Force-Based damage.

It's warp ammo that does extra damage to targets that have been primed for biotics.  Phasic ammo does extra damage to shields/barriers and is useful for:

• single-shot sniper rifles like the Mantis, so you can drop a shielded Marauder, Centurion etc. with one shot;
• biotic characters who want to be able to shoot through shields quickly, but who don't want to use disruptor ammo because it primes tech bursts that are weaker than biotic explosions.

Hey, it's only 3 buttons, what could go wrong?

I've corrected my 3-2 to 2-3, but I rarely had a chance to show off with full combo, basically it takes an Atlas, everything else dies too fast. I had a blast on my Sentinel, so it's a serious contender for me for my main. will feel really sad to promote him, he ended up on level 19. I might screenshot his build for further reference, it works well for me. Actually got my first silver zone on him, because I fell in with some nice guys, and just kept changing the equipment in the lobby. And, well, they queued up for silver.

I got a quarian infiltrator card, but I am not sure how useful Sabotage is going to be. so I now have a variety of species progression available to me once I work through the human kits -off Sentinel, off infiltrator and off Vanguard.

Okay, Vanguard is very, very, very fun to play though more than a little suicidal. Kind of trying to roll away fast after the whole v.complicated leap and Nova combo. Certainly no leaping at bruits. And very easy to get totally over-extended and far away from any objective. Oh, sometimes people would drop the lobby when they see a low level Human Vanguard, ha-ha. But, OMG, certainly fun in bronze!

These are only about vanilla human kits.

Soldier:

Adrenaline Rush: Automatic reload, emergency shield recharge (6A Evo) and damage boost/reduction (4A Evo)
Concussive Shot: Easy detonator and controller, cannot be used in AR (Unless 6B Evo for AR)
Frag Grenade: No-cooldown detonator

Highly dependent on gears and weapons
Very effective at using low capacity, high-damage firearms (Claymore, Raider, Black Widow, etc)


Infiltrator:

Tactical Cloak: Aggro remover, superb damage boost, overrides cooldown
Cryo Blast: No damage, but strong debuff and effective controller
Sticky Grenade: Primer and detonator, a bit difficult to use

Dependent on gears and weapons
Effective at using shotguns and snipers (Former recommended personally)


Engineer:

Combat Drone: Drawing aggro (Effective against LOLGeth)
Incinerate: Armor debuff, fire primer, detonator
Overload: Crowd Controller, tech primer, detonator

Better to keep light weight (Pistol/SMG)
Hide and deploy drone, shoot, use powers to control, debuff and create explosions


Sentinel:

Tech Armor: Damage reduction and power boost (for throw)
Warp: Biotic explosion primer, detonator, powerful debuff and DOT
Throw: Strong controller, can instantly kill/heavily damage humanoid enemy (out of map/to the wall), detonator

Better to keep light weight (Pistol/SMG)
Activate armor and keep it, shoot and throw humanoid enemies, warp, shoot & explode bosses


Adept:

Singularity: Crowd control, no-brain biotic explosion primer, detonator (6B Evo)
Warp: Biotic explosion primer, detonator, powerful debuff and DOT
Shockwave: Most powerful BE detonator, distance limit, can create multiple explosions (w/ singularity)

Better to keep light weight (Pistol/SMG)
Long distance: Singularity, shoot, warp = explosion, (w/ 6B Evo) warp again and walk away = 2nd explosion
Middle/short distance against single boss: Warp, shoot, shockwave = explosion
Middle/short distance against crowd: Singularity, shoot, shockwave = 2 explosions, warp again and walk away = 3rd explosion


Vanguard:

Biotic Charge: Damage Reduction, instant traveller, detonator, barrier recharge, damage boost(weapon or power on 5th Evo), suicide (when used inappropriately)
Shockwave: Don't spec it
Nova: Crowd control, invincibility frames (w/ cancelling technique), universal detonator, drains barrier

Two ways to play as I know:
Traditional novaguard: Keep light weight, charge & nova, use cancelling to keep yourself alive
Claymoreguard: Charge & Claymore, nova for control and detonation, use cancelling to keep yourself alive


I don't know which can be "stronger".
Soldier and infiltrator ask for good weapons, adept and vanguard will cost you some time to learn. The easiest vanilla human kits IMO are engineer and sentinel. But all of 6 are very powerful, indeed.