Well there were the 2,000 troops on the three Vulcan ships, but what about the cloaked Warbird escort?
While 2000 troops doesn't seem like a lot verse a planet, all they have to do is hold the government and a few key locations for long enough to have a full on claim to bring in the Romulan fleet as backup. Starfleet can't reasonably do something like an orbital bombardment. And there is no telling what the Vulcan's logical reaction would be in this situation. If the Romulans already have people in place on Vulcan, they might already hold a bunch of key places and just need troops as backup.
While 2000 troops doesn't seem like a lot verse a planet, all they have to do is hold the government and a few key locations for long enough to have a full on claim to bring in the Romulan fleet as backup. Starfleet can't reasonably do something like an orbital bombardment. And there is no telling what the Vulcan's logical reaction would be in this situation. If the Romulans already have people in place on Vulcan, they might already hold a bunch of key places and just need troops as backup.