First of all, you know well enough that a dissatisfied customer is times more likely to voice his opinion than a satisfied one, thus we may view you and others asking for change as 'vocal minority'. Also, let's have a constructive argument here instead of a 'popular terminology-slinging', trying to point out the lack of 'evidence', shifting the 'burden of proof' and so on.
Whereas you represent the silent majority? You still have provided nothing to support that claim. You can try to weasel around that with an appeal to 'constructive argument', but the 'constructive' part of that generally does entail substantiating what you say.
Second, balance. As I understand you consider that casters are wastly more powerful in PoE than non-casters (which is debatable by itself, any class can solo the game) and want to bring their power level down. But why don't you want to bring non-caster power level UP? If the balance among classes is the thing a well designed game needs why not make every possible build of every class OP? Besides, none of the classes in this game is underpowered relative to difficulty, there are only varying degrees of overpowerness (the game is pretty easy after all).
My main point is - if every class is balanced around the idea that they should be able to overcome the same obstacles with the same resourses and time investment then there's no point in having diferrent classes at all. The only thing that diferrentiates them is the VFX and color of the abilities. Like in DA2. I advocate for classes to be asymetrically balanced, with having power spikes at diferrnt levels, diferrent strenghts and weaknesses etc. And with asymetrical balance there are always classes that perform better at any given time. I see nothing wrong with casters performing slightly better by the endgame. In this matter, PoE is better balanced than most RPGs IMO.
Power is relative to a level of difficulty, there is little point in powering all the other classes up if this subsequently requires all sorts of other changes to attain the desired level of difficulty. Given an existing situation, it is therefore a priori more efficient to reduce the power of the three Vancian classes, rather than increase the power of all the others and rebalance the difficulty level around that.
But more fundamentally, the whole Vancian system in my view just doesn't work very well. It may work fine in the P&P setting it originates from, but lacking a DM it just doesn't translate properly to cRPGs. The power of the Vancian spells is supposed to be balanced against the fact that they can't use them as often, which is managed by the need to rest. But neither PoE nor its predecessors have really succeeded in making resting a genuine cost, and by its very nature that's unlikely to happen at all; resting is simply to binary and coarse-grained a thing to be able to do that properly. Hence the argument for changing it up more, to innovate a bit and go for a system better suited to cRPG. This would also allow for more differentiation of Wizards, Priests and Druids at a more fundamental level, rather than (mostly) just in terms of the spells they get.
And by the way, nowhere am I advocating for making all classes identical, far from it. So kindly keep your straw men at bay. I want classes (and any other aspects of the game) to be varied, complex and interesting. At the same time, I want them to be balanced (against each other, against the rest of the game) and mechanically well designed as well. PoE is certainly a big improvement in this regard, but the Vancian casting system is an aspect that is still in need of being thoroughly overhauled.