There's never going to be a way for them to say "everyone who deals damage gets rewarded" while also saying "only people who do X damage get rewarded" because there will always be people who show up late and only get one hit in on the Boss, there will always be people just sitting around waiting to hit the Boss once for credit, and everything in-between. But I would say the game should err on the side of rewarding participation instead of not. It feels bad when you genuinely contribute to something but don't get the Boss drops from it, and it's REALLY irritating when getting things like Trade Bars is connected to collecting loot rather than simply beating something.

Also as has been mentioned, Tanks really get the short end of the stick a lot of the time, Healers to a lesser extent since most can do some amount of damage for Overland but obviously not as much as a dedicated DD. So having it be based on how much damage you do to the Boss already cuts out a number of people who are doing stuff on anything other than a DD. They really should just make it that any damage dealt to the Boss will drop loot, not base it on how much damage you do.

Use oakensoul/war maiden/deadly and spam jesus beam, get a box every time. Pure templar for more damage.