As for retribution answer me this, does your tank not getting damaged at all?
Of course he does, but once almost all the team is already dead so the retribution skill will not be really usefull since the fight is already lost anyways.
If you want to maximise the retribution skill, you need to pair it with a healer (or anything giving you armor), not when you are the last one standing.
As for Retribution itself and maybe things like Leadership and so on that start with tiny %, with mirror existing it's hardly an issue.
If you need at least 5 points to start noticing an impact on the gameplay, it means you need to tweak the mecanic a little bit.
There is no other real solution, you could say make earlier levels give more %, but then you will start having various bastard builds cropping up as well as diminishing returns on investment which is kinda counter productive.
Of course there are solutions but it will need tests and a lot of thinking from the dev team. But having a little flat damages on the skill can make it usefull at low level without breaking it at high level.