...and I made it clear they couldn't just give them any ability they wanted.
And i thought Zombicide was a fully co-op game!
I took the full skill list from the website and highlighted skilled with 5 colors - blue, yellow, orange, red and green to correspond to what danger level those skills could be used on, with green only being available to zombivors.
That doesn't actually work with the published survivors. Some have powerful skills (e.g. Shove) starting out and some get the same skills much later on.
Character balance in Zombicide is as much a "by feel" estimate as by-the-numbers one, especially since there are no objective numbers, and your subjective "blue" may be my subjective "yellow", and vice versa.
Looking at all the dashboards out there will give you a good idea of what skills shouldn't be available at 1
That approach isn't reliably objective because the published characters are all over the place in term of which skills they have and at which levels they can get them.