Seriously, have you read a 3e book, like at all? One of the biggest complaints of of 3e was that spellcasters were just as powerful as they were in AD&D, but lost all of their weaknesses, such as the slower initial leveling speed, great potential to blow yourself up, highly limited spell slots, etc. Spellcasters are all powerful gods in 3e, especially at the mid to high levels, and even in the lower levels, they were were rarely left without some kind of useful ability to turn the situation in their favor. They are actually better at personal combat than the melee classes, have an ability for everything short of traps (and they can just bypass those magically rather than disarming them), and they literally have multiple spells that basically are "I do whatever the fuck I want" (for example "Wish" and "Reality Revision"). The Adept, which is supposed to be an NPC class, is a completely viable class to play as a PC just because its kit is based around spellcasting over everything else, and its regarded as Tier 4 making it a better class than the samurai, a fully kitted out melee class, or even the fighter.