It’s already been mentioned but it seems like people have more or less skimmed over it, so I’ll mention it again.
In regards to Agni necklace modifier and Quick Cast, I think it’s important to remember that future ranks may or may not have fire element skills.
Thus, if you’re not planning on taking offensive ranks other than pyro, then you may not have as great of a need for quickcast as other wizards would.
However, if you go warlock after pyro, your warlock skills would be losing out without quick cast, although dark theurge would still be quite strong.
If they do introduce ranks at rank 9 and 10 that have fire skills, there’s no guarantee the modifier given by Agni necklace (a separate modifier is given for each fire skill currently) will be significant for these skills either. In that case, Quick Cast would still be helpful, even more so if these skills happen to be a charging skill (and surespell if it still takes a while to charge, or is a channeling skill).
So the decision to go wiz3 or not ultimately is going to depend on what you want to achieve with your build. The way I see it, when you compare wiz3 with linker, wiz3 would be a bit faster for soloing lone bosses, whilst linker would excel at mobbing and taking down two bosses at the same time (because bosses do like to move).
Of course, since nobody knows what r9 and r10 will bring, there’s no definite answer. There’s also always the chance they either nerf or buff Agni necklace again, or just change values for each skill in wild directions. As demonstrated yet again, IMC can make classes/combinations way more viable overnight.
Nonetheless, here’s a video of an iToS wiz3pyro3warlock. No idea on gear or attribute % but I can imagine they’re above average at the very least.
(Also, is there any actual evidence yet that is accessible to say that the Agni necklace modifier is the same tier as Quick Cast or vice versa? I backtracked some threads but still can’t find any tests with quick cast.)