Especially playing a merc like Sawbonez, you want to heal after the fight. Now that the window has been reduced, I think the XP you draft is even more random, because the first few seconds after a heal the enemy is most likely dead or you are regrouping. Aura plays differently sometimes where mercs can ride the health station, but point healers run out of healing.
Also the difference between competitive and casual is significant. A medpack healer is way less effective with 7 teammates than he would be with 4 teammates. Area healers scale up better.
I realize it might be much more difficult to keep track of XP previously earned, but I think the result would be more payout for good medics and less randomness. Additionally, the amount of drafted XP could be scaled to the amount of healing done.