If you tell your audience that you're going to make a D&D game based on the 5e ruleset, as faithfully as possible, then you have an obligation to do so and to not change things or deviate them from that unless it's truly necessary to make the game work. If they had implemented thee ruleset 80% faithfully, very few people would be complaining - I'd be happy, for one thing. They have not done that; not even close. Whoever is telling you that they've done an 80-90% faithful rendition of the ruleset is straight up lying to you.
The problem is that setting a game in particular setting, using (or claiming to use) a particular ruleset, and placing within it creatures that are the defined property of that game's licence with representations within that ruleset... all creates an expectation that what is presented will actually be the thing that it is claiming to be - not something else that uses its name and (sometimes) appearance, but is functionally completely different.
If they want a creature to do a certain thing, and they don't find an appropriate D&D monster to fit that niche the way they want (unlikely, to be honest), then they absolutely have the freedom to make a new monster that DOES fit exactly what they want! They HAVE that freedom! If they want to make a special kind of troll that does fire damage is immune to fire, bleeds fire when you cut it, and does not have its trollish regeneration suspended by fire... they can do that! No-one (almost no-one, probably) will complain! ... As long as they don't call it a "Troll". As long as they call it a name that suites the new creature that is - call it an Emberwrack Troll, or something of that nature... fine; that's a-okay.
What's not okay is placing iconic D&D monsters into the space for players to fight, but then not having them actually be those creatures; it adds nothing of extra value to those who don't know better, and only makes those who do know better annoyed - you say you're fine with how they've been rebalanced, but you admit yourself with your own comment that you don't actually know how they've been rebalanced, or how they are meant to be in the first place. That's okay, but what it illustrates is that you'd have been happy either way; you'd have been happy if the creatures presented in their current state looked a bit different and had a different name. You wouldn't even know the difference. So why; why in the world would you support decisions from them that make no difference to some people's enjoyment and take away from others, and add no positive value experience over a difference choice, to anyone? Because that is what we have here.
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To Rag; It's LARIAN'S fault that there is no CR 1/4 illithid-themed enemy to pitch to a single level one character as a fair encounter... It's their fault entirely because they are the ones who created the situation where such a thing was called for, but, as our DM, as you are so fond of referring to them as, they didn't create a suitable creature to fit that need. That's their job, as DM. If they had a scenario, and looked in the monster manual, and couldn't find a creature suitable for their needs, and a re-skin and block-borrow would not suffice, then it was their responsibility and duty as our DM, to Make one for the scenario they had envisioned. They Didn't do that, and they are Not doing that, and by and large that is the problem.
I'll point to solasta again here, just because - They only have the SRD to work with, and so they don't have license for the complete monster manual. This means that they've had to build monsters to suit their scenarios and situations. They have done so, creating creatures that obey the general D&D design rules and principles, creating stat blocks that fit their CR and which, while unique and new, still nevertheless feel like creatures designed for the 5e ruleset, and which work as such, often utilising many of the traits that you'd expect such a creature to have (Like their little winged dragonette-type creatures having fly-by, for example). The result is that even though these are all new creatures with their own names and appearances, they still feel like 5e monsters, through and through... compared to BG3's monsters which, Despite having the visually distinct iconic appearances and names, do Not, in an alarmingly high number of cases.
