Damage Boosters are stupid all round, I personally say take them out of the game completely, or at least disable use in PvP, they make it so that the example Quagmire1234 happens quite frequently, and actually brings into question the whole point of leveling if someone 50+ levels below you can one hit you. And read the description of Damage Booster, it says "monster" in the description, not player, so that to me says it had an original PvE intent.
Now for the 15-20 level autohit cap, I strongly disagree on this one, do that and there's be no point turning up to DCS unless you're 140+ if a SINGLE 160+ turns up, because that guy would be invincible, keep the normal hit system as it is, the better fix would be to sort out Defense cap and sort out HP gain per level, etc for all Classes.