In ultima, the OT should not even hit the boss at all imo. Because 1. You will over-aggro the MT; 2. Your DPS as a tank doesn't amount to much anyway; and 3. You need the TP and place more focus on your surroundings (e.g. such as orb).

It is better for the OT to just pause in the middle.

Also, back to OP point/issue. It was the OT's fault. Even if you are doing badly, and even if you can't keep aggro or even if you are not using any enmity combos - The OFF-TANK should always accommodate the raid, so does everybody else for that matter. In simple terms, it is called teamwork. True as it may be that you could be the one sucking, but if you taken the initiative to work with the team, you are doing it right. Now, it's time for the team to work with you.