"If we knew what we were building, it wouldn't be called research!"
Sufficiently advanced mathematics is indistinguishable from magic
You see, the flavour is that when you tap exhaust him, you're sending him to go and spar with the other creature, teaching it to get better at hand-to-hand combat. Alternatively, you can just tap exhaust him to attack. He can do the first thing (exhausting to spar) multiple times a turn, but the second thing (exhausting to attack) just once a turn and only if he hasn't yet been exhausted.