I'd also rather only keep track of XP at the end of mission to reduce bookkeeping and take focus away from dealing damage as often as possible (so basically, no kill or guardian assist, and not XP for damaging opponents).
Does it seem reasonable to you?
That seems really bad, I hate to say. Getting XP for damaging the ships is really big. It probably doubles the XP you get in a mission. I would not recommend it.'
What we do is just track XP as normal. I went to the $1 store and got a bag of those little glass tokens. We toss them out when someone gets XP. I jokingly call them "Scooby Snacks". At the end of the game, we just dump all the tokens in the middle of the table and divide them by number of players. If there are some left over, we just give the left overs to the lowest PS pilots one after the other. So....if 4 players and 3 left over, the 3 lowest pilots get an extra and the highest doesn't. If someone said, "Dang...I'm one point away from <x>", then I'm sure we could give that guy an extra one.