Was the trial a mistake?

I am not sure, I know two people that were not going to buy the game buy it because of that demo. The way I look at it the way the review embargo worked was a bigger problem for there were different groups that had access to different levels of content so reviews could go all over the place.

No matter what Bioware did, the game never really had a snowball's chance because it was being released into a slew of old "fans" that were already dead set on rejecting it.  They had made it abundantly clear that they didn't like the premise of going to a different galaxy and nothing short of a rewrite of ME3's ending was going to satisfy them long before the game was released.  Many of them were in the media and had large followings.  When the base premise is disliked and widely reported for so long before release, it is pretty much inevitable that the reviews will not be as positive as when the premise itself is liked.  When people start something with the idea already in their head that they are probably not going to be impressed by it... they usually aren't.  The "wow" factor just doesn't get a chance.

There were people on the old BSN who were sayings long before release that the game would have to be pretty much perfect to get a good reception... to overcome all the negativity already there at that point.  Every previewer would have to have been absolutely blown away and making stellar reports.  They weren't.  The game wasn't perfect.  How imperfect really doesn't matter.  Only "perfect" would have made a difference.

I'm also convinced that some people who got the demo did so just so they could "race" to the internet with their memes pulling the game apart.  So, OP, I think in this setting the free trial was a mistake.  Knowing that the game wasn't perfect and that there was a crowd of people just itching to pull it apart, they should have possible just gone with a straight full release... preferably six months after they actually did release it and in a far more polished state (but I just don't think EA was giving them that option).

An actual argument there would be nice.

To answer the main question "Was the trial a mistake?" - yes, absolutely it was.

The game was not polished and, while technically playable, not up to the usual quality you'd find in a BioWare game at release.  By allowing early access to a game that was already not in a presentably "finished" state you allowed the game's "hype" narrative to get away from you and get hijacked by a bunch of YouTubers with zero enthusiasm for the franchise that would gladly overemphasize (close-up  shots, slow motion video, etc) the game's initial superficial shortcomings to boost likes and feed their Patreon profile.  What it meant is those potentially interested in buying the game near launch lost interest and moved on.

If BioWare/EA wanted to provide a trial that would have boosted hype and ramped up interest in the game, they should have made a free demo available on XBox, PS4, and Origins that would allow someone to play the game through Habitat 7 right up until the point where Alec Ryder transfers the helmet to Scott/Sara and you are just about to wake up on the Hyperion.  In this case, it would have allowed players to experience the premise of the game along with the jump jet and revamped combat while keeping them on a linear narrative track.  The mission is tight, fun, and focused in terms of a clear objective but allows you to explore within the map. 

The more I think about it, the more it makes sense that EA just wanted the thing out and over with and wasn't really concerned with the legacy of the game as much as the time it was released being able to provide needed revenue (4Q 2016) and cover the cost and marketing of the game.  No one concerned with a game's legacy or marketability allows the game to get previewed in an unfinished graphical state like that unless they projected the EA Access dollars it would generate would be enough to boost the subscription service in the process while believing that, despite potential comments about what players saw, that pre-orders would remain relatively constant.  

In the end, like what has been lawfully disclosed to shareholders during the investor meetings, the game was a significant contributor in driving revenue from Q4 2016 through Q1 2017 and most likely ended up profitable but, in EA trying to squeeze whatever dollar they could upfront from the game, they effectively paralyzed the game post-launch so there was no momentum for SP DLC nor immediate sequel.

Oh, there were a bunch of people willing to tear the game apart since it was first launched. A lot I suspect were people who were still angry about the ME3 endings.

Of course not, because the Bilderbergers are just a smokescreen. The Illuminati and the gray aliens are the ones really behind the conspiracy against Bioware. 

Yep, this was me. Preordered MEA, was super excited to play it, had no beefs with Bioware about ME3 or anything else (on the contrary, I love Bioware games and ME3 in particular is my favorite game of all time), was even engaged through my first SP playthrough and first few weeks of MP... But once the novelty wore off I started to realize/accept how mediocre the game really is. Maybe not positively bad, but not very good either. I didn't play the trial, but there wasn't anything in the first 10 hours that would have discouraged me from buying MEA if I had played the trial. Can't speak for anyone else, but from my own experience its hard to believe that the trial can be substantively blamed for MEA's underwhelming critical/financial/etc. performance. The lackluster characters/plot/world/etc., the borderline broken state of the game at release, and the impotent nerd-rage of anti-SJW crybabies, make for a more than sufficient explanation so far as I can tell. 

Who's blaming the players? They're just pointing out a bunch of people didn't like the game before it even came out.

And there were people who did that.

Um, no, not really. A minimal (~50% or so completion) SP playthrough took maybe like 5 days or something? And I played MP off and on over the course of a few weeks. Maybe it was spread out over a longer time period, but in terms of time logged in the game, it was not very long at all. I don't tend to form judgments of games/books/movies that I'm taking seriously on the first go-around, since its easy to miss alot. Its the 2nd run that usually cements my judgment either way, and that's exactly what happened here: I could barely make it halfway through a second SP playthrough.

Yes.

Playing the trial now, I have seen some Omega dance moves once or twice, but they were just quick flashes - perhaps fixed in patches (my trial is v1.10).

The facial animations are not good. But, they aren't so terrible at some points that you want to take your eye out with a fork.

Nothing I've encountered in this patched game has been OMG THIS IS BROKEN. There have been many substandard things, but were the game released closer to this patched state, much of the wind would have been taken away from the critics and the criticisms of the game would have been focused on a smaller laundry list of necessary patches from this point. Like Asari. Maybe a better base head model for Male Turians that doesn't remove most of their breathing apparatus from their face. But it would have been more nitpicking, like these, and not fodder for the lulz crowd FTW YouTube brigade.