First timer POV on the Cast on X nerv

As the title says I'm a first timer in this kind of games, so take my feedback with a grain of salt. But since most people complain about "my build is broken, where is my respec", "ggg doesn't care about us, they destroyed my build, now i quit the game" or my favorite "Why my build and not this other build that is much more broken", I wanted to provide a more gameplay oriented feedback.

The short version would be:
The nerv was way to harsch and needs to be diled back quite a bit. I understand where it came from, when I played frost sorcerer, I thought that there will be some changes in the near future, but no one expected the Spanish inquisition.

The long version:
For the first time I entered the realms of ARPGs and I was really pleasantly surprised, how fluent the progress on my Frost Sorcerer was. Every new skill that I've obtained had great impact on my playstyle, making me rethink my approaches to trash mobs and bosses. Every skill offered some sort of a solution to what I was missing and Cast on Freeze + Ice Comet were the final puzzle piece for my fluent gameplay. Up to this point I felt like my DPS is quite descend, bosses dropped relatively quickly and deaths were pure skill issue, but clearing the trashmobs still felt tedious. Cast on Freeze + Ice Comet solved this final issue and I finally felt like I've had a finished build and now I can go work towards my gear.
This is where the Patch blew almost all of my euphoria away... Now I'm back to the point where Bosses are still not an issue, because on those my build did not change at all, but the tedious killing of grunts returned and I don't think that it was a mandatory nerv.
When I first started using COF I didn't trigger in on each freeze (1 freeze charged me up to 95%) and it was enough top provoke this "something is missing" feeling. With mobs generating somewhere around 5-12% buildup, those 2 skills became almost worthless imo. Ice comet has quite the cast time, so it doesn't feel good to use manually in general, while COF equals in one skill disappearing completely and appearing absolutely random. It feels unfulfilling to see such a strong and (as it is right now) rare cast (which you've been charging on 2 groups previously) like the comet being dropped on some random, singular mob, instead of the potential rare mob or bigger groups in general. I caught myself kiting a singular mob for a minute or 2, for it to drop the freeze buildup, so the comet won't be used on it and leaving me with 0 charges on the next group.

Suggestion:
The buildup should be increased a lot again, maybe not to the point where 1 point in Meta Skill Energy is enough to get to 100, but I think the 100 should still be possible without farming the entire Skilltree for it.
Edit: The Energy gain should be the other way around, more energy from small mobs and less from big.