I think it depends on how Frozen Legion interacts with instruments of zeal. It has both the spell and attack tag, so maybe that means fanaticism is constantly being refreshed by it, along with the +30% more damage from instruments of virtue? If that's not the case and you have to use a movement skill as your attack for fanaticism, it's not the end of the world but it kinda sucks in comparison.
The other thing is is it affected by second wind? So you'd get 7 statues and cooldown reduction? And is that worth a gem slot compared to a damage support gem? Maybe if you're using it as a secondary bomb but not a primary skill?
Also the frozen sweep attack the statues use appears to be exactly Sweep but without the added phys and knockback and with 100% cold conversion. So that means if you're getting cast speed, but keeping the base cooldown, you're just running around with a slightly weaker version of sweep. I think.
I think the tree for this will be far different than spell or RF builds, so if it does end up a fail you'd end up with an elemental attack build using conversion. I think Mathil has a bunch of those in the past for a loose template to follow.