I think the problem isn't that the wizards have been nerfed - but that they were OP in PoE 1.
PoE 1 Wizard had an exceptional weapon at level 1, +50% attack speed at level 5 , an fast AoE Paralyze with damage at level 9, and so on. In the late game, with a little of help from the priest, the wizard was this. It's sucked for me because I 100%ed PoE 1 with a wizard and the nerf-hammer has hit me hard when I wanted to continue playing with him in Deadfire, but it was something that had to be done.
This doesn't mean that the wizard is fine as it is at this moment: it has some useless spells ( Eldritch Aim anyone? ), undertoned ones (it's becoming harder and harder for me to justify summonning a weapon, and lacking in passives (though this could be just me).
But it doesn't mean either that it is weak: it's hard and requires a lot of knowledge about what you're doing, but there aren't many classes able to deal almost any type of damage (fire, corrode, slash, freeze, crush, pierce - you name it, and the wizard has something for you), which is important given the DR rework, to target any type of defense, and to cast 5 buffs on themselves in 2 seconds. While other classes excel at a given mechanic, wizards are the jacks of all trades.