I actually had no idea how HE's and CPS aoe stacked against each other. Imo If you look it that way, then yes, ability becomes extremely situational compared to what it used to be. Also doesn't ISU have some kind of hard limit of how much models it can kill with one shot?
Afaik, there is no hard limit to damaged or killed models.
The previous CPS profile was very different from the HE shell. I understand that they changed it because a range 70 shot with large OHK radius is just frustrating and unfair to play against, but at least the ability was providing a different shell.
It is obviously not the same as the HE or the AT shell, it is just very boring. Like both shells in one, a bit better and piercing, but you only get one shot. It does not really add that much anymore.
I am not sure how large the delay was before the changes, now it is about 4 seconds. Which opens op the possibility to cheese a normal HE shell followed up by a CPS slightly behind the retreating team weapon.
As an easy fix, I think it should just get cheaper, and increase the CD if necessary to prevent spamming. A more complicated fix would be to craft a completely new ability. I could imagine something like an AT focused stun shot, owing to the large caliber or so.