Try running an Adept through some encounters, especially at lower levels, and you'll quickly run into problems because you simply don't have enough to do with your actions. I've only played them as a DM, but their typical play pattern tends to be either "Unload all your spells in one encounter because you're an NPC and you only have one encounter per day" or "Conserve resources by only casting one spell per combat, maybe two if the second one is 1st level, and then fire a crossbow for the rest of the fight." Sure, you can unload a
lightning bolt or
scorching ray...once. And then you're spent. It's not a role you can play on a consistent basis. Maybe you look okay in one encounter, but average out your performance over four encounters and it looks a lot less impressive.