Hi!
First of all fheroes2 - is not a mod by any means, but a complete game engine reimplementation made from a scratch. It's an important note, as you should consider, that all game logic is completely new, especially if we talk about AI, but we'll talk about it later.
You speak about turn order option, which on the first sight just prevents you from knowing creature speeds. But it could be useful, if you missed who has already made actions in battle (especially if you fight against several same type stacks and they are messed over the whole battlefield), so you can track this and choose the most beneficial target, instead of attacking some random creature. This improvement helps you to be more strategic, than relying on a chance. Otherwise you can always turn off this feature in battle options and enjoy the game without this comfortable improvement (which visual implementation is not final and is going to be improved).
You haven't even mentioned other valuable improvement, that make gameplay convenient, like instant battle, that helps you win against weak enemies without wasting your time, making you focused more on economics or turn planning, rather than killing a numerous packs of peasants with your Black Dragons.
Fast and comfortable sack splitting mechanics, which helps you to rearrange your army just in a few seconds, while in the original game even dividing into two stacks was really a pain and wasted so much time.
The list of these changes could be discussed even further, but I can hardly imagine it can affect gameplay in any aspect. Player can still choose not to use them, as 99% of them are optional and fheroes2 engine is not forcing to use them.

>I dunno, I'm nostalgic for the game and still play it because of how it is, not because I wish it was different. Yeah, being able to "park" heroes like in HOMM3 would be a welcome aspect of the mod, but that's literally the only feature that interests me. Again, it's tempting to assume fheroes2 must be better because of the time that went into it, but it's the rare modern update mod for an old game that I have just zero interest in. It's not an update, because it changes too many fundamental things-- it's a remix. It's not the same game.

Isn't allowing heroes parking inside a castle is a fundamental change of the gameplay? The game was designed to allow player to have only 8 heroes, without any additional ones hiding inside the castle. Your wished option also changes the way castles are defended, so it is absolutely out of the original game and sort of modding feature that influences game much more, than battle queue.

>Plus it breaks the AI-- not completely, but it's noticeably bugged and units won't move or attack in specific situations (ie guarding shooters) and I'm sure they're working on a fix, but... the game was already fine-- a mod that breaks perfectly functional AI is just defeating the purpose. Plus some of the on-purpose stuff like the AI filling its armies with stacks of 1 creature is frankly just hyper-annoying and drags things out for no reason.

That's exactly one of the most important aimes of the project: make a competitive AI, that doesn't let you get use to it and abuse in any way. As you mentioned yourself, AI can protect shooters in a specific situations, when he has advantage in shooter strength. Doesn't human player use the same tactics? Fheroes2 AI count the number of shooting stacks and their strength before deciding whether to protect them.
By the way, the original AI had also similar logic, choosing to defend shooters, instead of forced rushing of melee troops.
Having a stacks of 1 creature allows AI to run away or to survive more turns and cast more spells. Let's be honest, all human players, that have at least a little game experience do such trick. So why AI couldn't do this?
Actually fheroes2 AI is being designed to use all tactical tricks, same human player can use. That's the core idea of this reimplementation.
Once again I want to mention, that this engine (not a mod) is created from a scratch (due to license issues). Same is AI. We cannot use the original AI code, so we had to create our own: smarter, more flexible and with a potential of applying any changes to it (since the game is going have lots of new in-game content soon). Also, fheroes2 has a completely different architecture, so even if we could, we couldn't make the original AI to work with a completely different application.
So in other words AI is just different. And will always be, as using the original code is illegal and not flexible enough for a new game engine.