One- I have screenshots of GP gain when other team has 5k advantage and we are all downed
2- exploit or not combos should not stack from rear if team is down- We had a team downed and they stacked 200+combos while downed - revived at the end- nuked us with crazy combos and won.
There is no defense to this- so game mechanic or not - it is poor mechanic
If you down the other team and stack combos while up- well that isn't really better- but at least the team is up and stacking a defense
Counter to assist Combos: Stack your own powerful assist combos.
Counter to attack combos: Stop killing your opponents 5 minutes into the match.
No defense argument sounds more like you are too lazy to bother. Not a poor mechanic, rather you too lazy to use the mechanic for your own advantage .