to be fair the phase spiders & mud mephits are probably the most annoying fight in all of EA regardless - having said that having monsters use their attacks & special abilities as per the monster manual does make sense but its not the end of the world at least for me personally.
I completely wrecks any real sense of CR, and in fact, makes Larian's job even harder.
If they'd started with core DnD and then adjusted based on need, instead of starting with DOS and implementing homebrew rules, then they wouldn't be months behind on development, and in a scenario where balancing is all but impossible.
