What you’re referring to as far as being useful at level 1 is what I’ll typically refer to as “power spike levels”. For casters, that’s every new spell level unlocked, for martials it’s when they unlock extra attacks, reliable expertise is a big one for Rogues, etc. it’s bad if they’re excessively delayed and the character is only spiking at level 10,11,12.
The monk, in truth is a 4 Rogue/8 Monk and starts as a Rogue. Because we are talking Drow/High Elf Rogue/Monk you get perception for free as a racial. Really ends up being a way better rogue than Astarion - because you always put them in front and they WILl catch every ambush before it happens since they almost never fail the perception checks. They are always in front of the turn order and make a solid Tank as well. Just make sure they have the Hellrider Longbow - it will give them advantage on perception Checks (ACT 2 Item)
Otherwise you gear them as a Monk and at Level 12 you are doing 200-300 damage per round.
The Wizard I would propose is never not useful since you get the Hill Giant Strength potions as soon as you get to the grove so they maintain a high power level - even at low levels as a skirmisher doing 8-18 damage per hit with a Greatsword, and also having close in Evocation spells that only really work on the frontline anyway. Later they will trade the greatsword for a staff of some sort but early on you work better as the Skirmisher and need less long rests.
