BG3 should split up XP according to your party, I don't see a reason for this not to be implemented. Your logic also also flawed, as if you have 5 party members you also only get 25xp.
In answer to your question, what is the point of the license if you don't use 5e rules? D&D is difficult by design, we should not be encountering Imps, Intellect Devourers or Owlbears at the level we are in BG3. I have been hiding to kill the Intellect Devourers which should not be possible at 1st level "The intellect devourer can sense the presence and location of any creature within 300 feet of it that has an Intelligence of 3 or higher, regardless of interposing barriers, unless the creature is protected by a Mind Blank spell."
Larian have cut xp due to the monsters they have put in the game, in my opinion too early. They are devaluing the monsters, Owlbear only getting +5 to attacks when it should be +7. There are loads of 5e rules they are not following, the Rangers duelling passive +2 damage is also not being applied. It's a joke how much they have wrong, I just hope it is all fixed for release.
I agree that BG3 should split XP evenly between participating party members. But I'm currently just reporting what is actually happening. Larian is balancing the game for a party of 4 and BG3 encounters give equal experience to all companions regardless of who participates in combat. Party of 1? 25 exp to *all* characters, calibrated to level up your party such that a party size of 4 remains of appropriate strength for encounters. Party of 5? Same thing.
Misrepresented monsters is, as @Womerine says, an entirely different issue than xp. Players familiar with D&D will approach encounters against certain enemies in specific ways, based on foreknowledge they have of those monsters. But BG3 sometimes drastically changes their abilities/stats without changing their names. Some argue this is a good thing ("new and unexpected = good"), and others argue this is bad ("I'm being punished for being knowledgeable about D&D, in a D&D game!")
Xp, however, is different. Unless you're selectively fighting encounters based on how much XP you think they'll give, it doesn't change how you play the game, just how fast you level up. As others have said, the tradeoff is # of encounters. If Larian increased enemy XP to match MM, they'd have to drastically reduce the # of encounters in the game. Imo, monsters having non-MM experience is a very small price to pay for more content.
