The double issue comes, imo, from the way damage is applied.
Snipe beceaus of his range, spit beceaus you can apply it, even stack it, and continue with you auto attack.
Some attacks are just to powerfull in the way there applied.
Where snipe would be the most powerfull early game.
Tbh, most abilities are scary when you double them.
So its more fun to have 1 of each class.
If you have two of one class, your basicly using them as one person doing double damage. And this for some classes is op.