Thanks everyone for your generous input. You have convinced me that the Tremere are balanced. I'll summarize what I take away from this discussion regarding a Tremere not holding his own sigil:
-You can design a starting Tremere whose parens has passed, and who is thus holding their own sigil (and those of his filii).
-Tremere operate as a power bloc, which benefits young Tremere if their goals are aligned with those of the house.
-Tremere are playing the long game. Right after gauntlet, you are at the bottom of the house, but you can rise higher than in other houses.
Regarding the other singularities of the house, I would say that
-Material support and tasks for the house are supposed to balance each other out.
-Tremere may have a second magical focus, in addition to the minor focus on Certamen.