Kotor 2 has terrible mechanics and combat. Stop using those drugs man...
I honestly don't know how you can see this obvious truth so clearly, but defend the exact same combat model in the IE games. Kotor actually had more options too. Please explain the differences that made one good and the other clearly bad.
For starters, KOTOR1 is like 5 years after BG1. I don't think that the combat systems are really that close. In BG you have a party of up to 6, and the lethality is much higher, everyone who has played it knows it. I'll always remember how you can clear the boring, repetitive final stages of KOTOR2 spamming Force Wave. You can't do that in BG or IWD, you have to think a bit.
In KOTOR2, too, you can practically turn your whole team into Jedi, which helps them. In BG or IWD, a rogue was always a puny rogue and had its specialized uses but wasn't an all-capable combat machine.
I think that your whole argument is built upon "hey, KOTOR uses something like the d20 system, it must be the same as AD&D2!". No it's not. Even IWD2 is not the same as the rest of the IE games.