So then what happens when a player uses only a party of 1? That makes all the encounters too difficult and so Larian has to change the encounters to keep them from being too difficult, right?
I think most of us who play solo like it for the challenge and don't want the game to be changed to make it easier, takes all the fun out of it.
There was a whole discussion about this...maybe earlier ITT, maybe in a different thread. But while you play solo for the challenge, that doesn't mean everyone or even most people who play do. For example, some people may just not want to go through the hassle of controlling multiple characters, especially with Larian's toilet chain.
As always, this is easily solved by options and exp splitting. If you want to play a challenge solo mode, don't enable exp splitting and level up at normal speed. If you want to play a normal-difficulty solo mode, enable exp-splitting (and/or Lone Wolf). It'd take Larian ~zero additional effort to make such changes optional instead of mandatory settings.