Leaving from Earth with the Ark ships isn't going to work...

One does not simply discvoer plot device before time.

Plus Bryson's work (in the Leviathan DLC). Thing is, it took nearly all the combined fleets to destroy one Reaper ... which merely delayed the Reapers. In Arrival, destroying a mass relay delayed the Reapers a bit longer. Adding Quarian and Geth fleets will help slow the Reapers down, but are not sufficient to stop them from overwhelming the combined galactic fleets.

You're not going to build, man and train a galactic fleet capable of beating the Reapers, in the time you have left ... even if every ship is equipped with Thannix cannons. Or build planet-based defense systems, capable of fending off sequential, system by system Reaper invasion ... methodical, plodding, unrelenting Reaper invasion ... i.e. defeat in detail. If you find it implausible that Council races could build Ark ships in the time left, after the defeat of Sovereign, then building planet and space based galactic forces capable of defeating the Reapers is well nigh impossible.

So you seek out alternatives ... Reaper killers (Leviathan), unconventional weapons capable of destroying the Reapers (Crucible), enacting "continuity of civilization" alternatives (Ark ships) ... not putting all your eggs in one basket, but placing bets on as many options as possible, which might pay out, prior to the Reapers arriving ... or after.

Because the Reapers are not that far away ... years or months, not decades, not centuries not millennia ... the decision was to do this without making it widely known to the galactic populous ... perhaps to avoid mass panic. This McGuffin (plot device to further the narrative) is a bit hard to swallow, but at this point, hiding the true nature of the first Citadel attack is baked into the cake of the MET ... "ah yes, 'Reapers'" ... so there we are.

they couldn't take direct control of the relay network to let them, the citadel controls the relay network, and the council had locked out all but one route to the citadel after sovereign's attack, so the reapers didn't know what that route was...


them screaming towards their main enemy (earth) makes sense to a degree, about the only thing that didn't make sense was it taking more than a few days for them to hoover up /destroy earth, there's literally zero chance that such a heavy invasion of a planet would take so long to be finalised... but once you skip past giant plot holes like that its all good

and yeah it also doesn't make much sense that they wouldn't of seized the citadel unless glowbrat was ordering them to other tasks, I mean isolating every relay to prevent any sort of organised resistance would of made perfect sense .... which means either the machines were toying with them because fear and loss of hope makes them taste better or there far from superior to organics .....

To be fair, without help from Cerberus and Feron, she wouldn't of done anything.

Shepard: What was going after the broker have to with finding a way to stop the reapers?
T'soni: I was so obsessed with finding the broker, that I completely.....forgot.......
Shepard: Hmm. Is that the same reason for having my armor on display in your apartment like its some kind of prize?
T'soni: Uhmm.....I.....I.....should go.

The reapers were made stupid in ME3 for them to be defeated. With the numbers they have, there is no way the galaxy would be able to stop them even with the plans for the crucible.

There is already a technology to travel faster than light. Welcome to Mass Effect.