She can have the highest AC of all characters if I recall correctly with spirit armour and mirror image, plus she can charm and guide people making skillchecks much more likely. The decoy spell works pretty nice, too. The mass sneak spell is also pretty good in certain situations. She is decent in melee, too, and isn't healing word only a bonus action? So you can heal and pick a party member up at the same time. But yeah +1 dex and +1 con would not hurt. She can still dish out some ranged damage with her two ranged spells with a decent hit chance, when you have height advantage.
She is rest intensive, though, I'll give you that, if you do not rest a lot she will be dead weight.
Yes for pure combat she is on the weaker side. But she has lots of utility. At 4th level I always give her the +1 dex and +1 con which fixes most things. She also has disguise self which can open up opportunities.
I suspect a lot of people overlook Guidance (in part because the conversation tips don't clearly display its impact) . . . its totally awesome and should be kept up all the time on your lead character.
