AC was traditionally seriously underpowered in AD&D and D&D3, at least on highlevel.
In BG2 ToB, it was basically pointless to try to stack AC unless you would go for Swashbuckler with Shield. Then you could actually reach AC -24, the hard maximum (AD&D uses reverse logic and lower AC is better). Everyone else would get hit all the friggin time.
The exact same happended with d20, by the way. In KotOR there was no point making a defense focused character, you would still be hit all the time anyway.
D&D5 is a huge improvement over this state of affairs.
