What I would suggest is increasing infested terran movespeed, decreasing the cost of them and decreasing the hatch-time. I suggest letting neural parasite behave like a tempest range attack, at least give it the rage, and cast while burrowed. This will make the overpowered units think twice and make protoss have to micro. Fungal needs to increase in duration I'm fine with the DoT rate though.
Lets look at this objectively, on a unit vs unit basis:
marines beat infestors cause infestors can't attack back
hellions beat infestors cause infestors can't attack back
maruaders beat infestors cause infestors can't attack back
You can see where this is going, so I'll just get to my next point. I think that infestors should have a ranged attaack of similar dps to hydralisk perhaps a bit more I am no mathmagician so I really don't know the specifics.
I would like to see all other zerg units move faster than the infestors so I can keep my infestors in the back. I too often see them moving into a meat grinder and I feel this cornerstone unit deserves a faster, sleeker army to go with it (but don't nerf infestor speed.)
I feel like the infestor should serve multiple roles instead of being target-fire bait like it is. I think as it moves it should spread creep instead of that goofy slime trail. This would allow the infestor to not die as much because there will be creep. They should get a passive ability to heal on creep too, sort of like roach burrow.
If you look at professional games you often see infestors dying left and right with one missed control this is unfair I would like more armour on infestors and maybe more hp so that they can actually live long enough to do some damage. It's ridiculous how fragile they are they are too easy to kill.
Thanks for reading this mr. rock I hope you have a good night!