BLMs usually pre-cast Thunder II or Fire III around that level. One Tomahawk is enough to get initial aggro and build an enmity cushion and let the DPS do their proper rotations without having to gimp themselves. In the case you provided, the BLM could've adjusted by attacking the 2nd mob paired up with the faces instead, letting the tank build aggro and safely drag it over to the platform. That is, however, a niche case where DPS control is needed. Whenever I DPS, I make sure to not attack the faces unless they're on the platform. Doing a proper rotation and having no sense of discretion are not the same thing. Otherwise, I go all-out in any normal situation, which is what the OP is talking about.