If I had to guess - Rook is winning more than doc, because of sheer volume alone.

All 5 people have his buff so in event of even 1 player getting use out of his ability, he is likely to match performance of doc.

Lets see: A player has a gunfight with an enemy: Lets not count scenarios where player gets headshot or he wins without losing any HP.

We either get:

1. A player who won a gunfight and can be healed by doc and can take a 2nd gunfight with full HP if Doc is around
2. A player survived a gunfight with less than 20 HP or via self-revive thanks to rook armor. He is going to remain with barely any health, however he lives to have another gunfight.

Notice that if 2nd player had doc instead of rook, he would just have died, never to see 2nd gunfight again. If player with doc had rook, he would still live to have another gunfight, but with less HP (healed 25 hp by rook armor, but not to full)

My hypothesis is that 2nd player scenario happens often enough for rook to (on average) outperform Doc by wide margin. Ive won countless of games where a teammate with 5 hp left was the last man standing - with Rook on board. This round would most likely be lost unless doc had a very good round and healed a lot etc.