I think they kind of wanted to have them be map-specific by design, a design choice I don't agree with. I think if this game had a massive PvP population, it would make sense to have map-specific rewards to motivate people to try other maps and not just queue up for the one they like. Though with FFXIV, the PvP queues struggle to have enough for two modes with a third on life support.
As such yeah I rather they just have had this mount be for Wolf Marks. If the cap is a limitation, they can always make tokens that can be bought and exchanged for mounts, not unlike mark logs. So they could have the flexibility of having tokens for 5 or 10k Wolf Marks or something and then rewards costing more than the cap could suffice alone.