Heavy Machine Gun/Infinite Ammo builds

There seem to be quite a few ranged AoE + ranged single target builds that incorporate fast cast and max mana regen.

I use Firestorm + Icespear on my Witch, for example. I max out on cast speed and mana regen skill pts. (and items)

This allows me to carpet bomb/machine gun, while refilling mana almost at the same rate I'm using it, thus never running out.

This can be fun, but it's concerning. It certainly makes PvE almost trivial (with some exceptions - multiple named Necro/Warlock mobs are still really hard).

It almost makes mana regen/cast speed mandatory because it's so powerful, homogenizing builds and classes.

btw, several classes have variations on this build

Poison + Burning Arrow, for example.

Also, another concern is that Str is underpowered, because Dex and Int seem to be the easiest to do this kind of build with (Firestorm and Poison Arrow appear to me - so far - to be the cornerstone of this type of build).