Is There Too Much Content For Liara?

To us, yes she does. To normal fans, maybe. To her fans(they are legions), No there is not enough content for her.

As mikaelnovasun said before me, the reason Liara got more content in ME 3 is not necessarly because BW loves her more but because she is the only previous companion from ME 1 or 2 to be sure to be alive by that point. Any writing, voice acting and programming that went into her content will be seen by the totality of the audience.

The suicide mission made ME 3 much more difficult to bring back old characters as the story needs to be able to go without them because they can be potentially dead. Even fan favorite tali was close to not be included in ME 3 because for many players, they won't access her content due to her death in ME 2. And even with her being present in ME 3, she only joins the normandy after two thirds of the game has been completed.

The average players (the huge majority of the audience) will at best finish the game once and won't bother to start it another time. If tali would have the role of Liara in ME 3 and she dies, it means all the ressources of writing, voice acting and programming made into her cutscenes will be wasted for a huge chunk of the audience.

There was no way that a character like Miranda or jack was going to get would get as much content as Liara simply because for the big audience it might be wasted ressources. A character that can potentially die will always get secondary role in the sequels and it kinda make sense as the story needs to be able to go without them.

The possible death of lelianna in DAO forced the developper with 2 options, either they make a retcon for her surviving the game regardless of what happen to allow her to have big role in the sequel... OR she gets a secondary role in any sequels to come. But the studio was not going to make 2 completely different advisor for the inquisitor in DAI in case she was dead as this would have been a huge wastes of ressources. No studio would put that much money and time into making 2 completely different characters that would be with you from beginning to end depending on a decision from a game that came out 5 years before.

Yes. At least in ME3. Some of the content she has doesn't make sense for her to have.

At the beginning of Mars she tells Shepard to get to cover. Why didn't Anderson do that on Earth? There were a couple opportunities for him to say that.

After talking with Hackett after Mars. Just have the game go to fade-to-black instead of having the whatever between t'soni and Shepard. 

The first dream. T'soni mentions the turians won't do anything until their Primarch is rescued. Shepard already knew that. No purpose for the asari to repeat that.

On Menae. Why is she the one telling Shepard about Victus, if Garrus is not in ME3, instead of General Corinthus? He's always there. He knows Victus personally. 

The second dream. Was it necessary for the asari to go to Shepard's cabin to tell her/him the salarian councilor wants to talk? Why couldn't t'soni use the intercom? Or was it faster to go to the cabin? Why couldn't Traynor or edi tell Shepard over the intercom?

I would add ME1/2 as well, but fortunately the game is setup where the player can deal with her for a very brief time in ME1. In ME2, she can be ignored for the whole game except the broker dlc, if the player chooses to play it.

I feel like Liara and Cerberus are often used as "easy" solutions to fill gaps in the story and/or gameplay. Though it doesn't hurt that she is a fan favourite. I have some sympathy, game development is usually hell, but at some point you gotta pull the plug.

My only issue with Liara when I get right down to it, is if you are romancing someone outside the squad in ME3 she still throws the blatant flirt at Shepard during the Citadel dlc. I tend to RP Shepard and Liara as seeing each other as family after their melds in ME1, and so I play the flirt off as her poking fun at Shepard. For how many moments she has with Shepard in ME3 when you do romance, she still refers to Shepard as just a friend in almost half of their conversations.

That's honestly one of the reasons I will go to the mat on Garrus having a better romance than Liara.

Especially in 3, but to some extent in 2, Liara keeps forgetting you're a couple or having no extra dialogue for romanced Shepard, whereas Garrus almost always has something.

Part of that is, of course, that Liara is guaranteed to be there so she has some exposition lines, but it really comes across a bit awkward.

It's not that there's too much Liara, it's that there's not enough everybody else.

Yes. Her role in ME1 makes sense and ME2 mostly keeps her in a paid DLC that lacks translations but there's way too much of her in ME3. That she's the only one guaranteed to have survived by that point doesn't matter because many of her roles did not need to be taken by *anyone*. No one needed to barge into Shepard's cabin, interrupt turian officers on Menae etc. There's no reason why Thessia was supposed to be more mourned than, say, Palaven. Shepard's combat-capable non-squad romances were perfectly fit to be the rescuers in the Citadel DLC. Some more examples were mentioned so you get the picture.

While not being the biggest fan of Liara I think she doesn't get that much more contents than most of the other "main" characters(like i.e. Garrus) and the biggest reason for this to begin with is overall probably her early introduction in basically every game of the trilogy. However it depends if you only count in her off-mission content or also involve her dialogue and role during missions and the associated cutscenes. It should also be noted that in ME2 she only plays the role of a minor character storywise.

If you're asking in terms of romance, well I don't exactly know. Like 8 years ago I once made a "Liara-only" playthrough of the trilogy, but I don't really remember anything of it. With LE, I romanced her in ME 1 but imo the writing felt a little awkward overall and the amount of extra dialogue seemed pretty low, too.
In terms of love interests, the role of the Shadowbroker DLC is somewhat interessting and has some content which you maybe could call blantant displays of favoritism. However some of it may be linked due to strict developement deadlines etc. What I'm refering to are mostly the conclusion scenes, where for example even rejecting Liara for another love interest will result in a quick peck from her and at least me for it felt quite strange that Shepard seems to be utterly devasted when Liara leaves the Normandy after rejecting her again in his cabin. You could argue that this implies that the "good" ending for this DLC is rekindling the romance between Shepard and her and not accomplishing this is the "bad" ending, but you could also probably make time pressure on the devs responsible for this binary kind of ending.

On a side note, the Shadowbroker DLC felt very similar to the character of Shani in Witcher 3's Hearts of Stone DLC(which I actually played before I first played through Shadowbroker) where basically rejecting Shani is more complicated than anything else and the ending always will at least result in a kiss.

Hmm. She may have been a favourite for old fans of the series, but I doubt that is true for people introduced to the OT via LE. I didn't decide to give ME a try until 2016 and immediately disliked her. That said I was in my mid thirties, so maybe fan age is a factor.
I'd be very interested in seeing the results of a poll from new players, and not old ones.

When I first played Mass Effect 1 for the very first, I romanced Liara but the more I played the more I was kinda turned off by her shameless flaunting and throwing herself at you especially in 1. So I turned to romancing Ash. Then ME 2 came out and I was hurt by how Ash totally dumped me, so even when playing I looked for someone else to romance. It was then that I discovered Jack, and I have romanced Jack (playing as default appearance of John Shepard) ever since.

Playing as FemShep.... I tried Kaiden's romance and I enjoyed it. For my FemShep playthrough it's either Kaiden or Traynor....and 9 x out of 10, I romance Traynor. But mostly I play as John and romance Jack. I see Liara as a really, really close friend but nothing more.

She does get mad if you do that.