Do they have Word as Bond? I think that's just speculation. If not, citation please.
Dramatically less profitable that actually achieving their stated aims: monopolizing a critical trade route and taking the march to ensure their safety.
They're nomads. Conquesting is a rare behavior.
So... he burns one of our provinces and we respond by giving him money. And he's supposed to be scared that if he burns more we'll... give him even more money? Paying people to not have to fight doesn't make people scared to fight you. Quite the opposite.
Again, Nomads don't usually conquer. This general and our civilization are a special case. Sure, it would free up military for further raiding, but this guys longer sighted than that. The Stallion March would set up those nomads for stability and prosperity for centuries, assuming they don't get WAAAGHed off it by someone else.
Given that none of the listed ones stand up to scrutiny, I doubt the ones in the etc. will.
He's being exceptionally rational; you're strawmanning by pretending the argument is that he's doing this for a grudge. Noone has been saying that.
He wants a monopoly position on trade, and he wants the positional advantage of the march. Both of those will strongly outweigh tribute in the long run.