Yes, DnD combat is heavily influenced by luck and forewarning. If you are surprised and have lame dice rolls, you are probably toast, even if you are a ninja ( with or without cheese ).
BG3 has a number of implementations in to reduce the impact of such randomness, more so than any other remotely D&D-based computer game in history, and more is likely to come with the implementation of feats such as Lucky - which probably will be brokenly OP in BG3 due to broken rest mechanics. I would argue Larian have gone much too far with the homebrew in this regard though, ie virtually guaranteed advantage, barrelmancy, all the implementations that easily trivialize most if not all encounters.
Ultimately though, BG3 is a computer game that allows you to savescum, it's groundhog day all day every day till you get it right. As such the need for a balancing encounters that accounts for bad-RNG, isn't nearly as required as in a tabletop game.
