Tamers can ride their Heilang and become completely invincible during the fights.
Only way to knock them off is to use BSR ability but by the time that can occur, a few matches has gone by and their CD to remount is up.
My fix is to prevent Tamers from mounting on their heilang during AoS battles. As for outside AoS, it isn't a problem.
I'd like to suggest that Heilang gets overhauled in general. The extreme DP while mounting him always seemed kind of weird. I'd much rather prefer if Tamer, while mounted, would be as strong as Tamer and Heilang fighting together without her mounting him. And I'd also like if he wouldn't feel so hard to move. While mounted Heilang should feel like a class on its own, rather than some kind of vehicle.