option 4 sounds appealing but somewhat unrealistic. I really doubt that encounters would just work well in all cases if monsters were their faithful adaptations - it might in some, but probably won't. Of course, I would rather increase party size, and rebalance the game appropriately, closer to 5e originals, but that is just not going to happen.
Oh yes. Absolutely. I agree that total RAW 5e stats and rules won't work. I'm looking for a much more faithful adaptation, not an absolute RAW experience.
For example, I don't mind various goblins. They don't all have to be cookie cutter goblins with scimitars and shortbows and all 7 HP with 15 AC. One of the monsters Larian has done well is goblins, imo. They've made them varied and interesting and not all the same.
I don't mind slight variations. For example, I think rock throwing harpies makes sense, but like Ragnarok said at one point on a different thread, I'd like them to actually have to find and pick up rocks and throw them. If they don't find them and pick them up and throw them, then they use clubs and claws and such. Maybe some harpies could carry clubs and others bones that have similar stats to clubs. Maybe some could throw bones and skulls. Maybe some could actually use a dagger or a spear. Whatever Larian wants to do with that.
The issues I have are with basic monster stats. I don't like imps that have no resistance or intellect devourers that can't devour intellect or have resistance. Even if the intellect devourers are baby versions, give them their proper name and make it plain that they are babies (ustilagors). Don't have phase spiders teleporting clear across maps some 300+ feet while spitting poison globs at opponents, thus changing the entire spider breed completely. If it's a phase spider, they should phase in and out of the Ethereal Plane and attack only at melee. Shoot. Call it a Misty Step Poison Spitter Spider and I'd be happy, but don't call it a phase spider and then have it not act like a phase spider.
But even with these, I'm fine with variations. Have 3 phase spiders that act like normal cookie cutter phase spiders but then have the matriarch act like some crazy teleporting poison spitter. She's a crazy mutant phase spider. That works for her. The others, though, should be basic phase spiders.
And who said it won't happen. They've done other major crazy things that we didn't ask for, like put a ton of time into creating weird mini-camps. Why not something like this? It can't hurt to ask for it, anyway. I mean, I won't hold my breath, but it can't hurt to ask.