I'm not sure that any studied watching of the series should lead you to conclude that they are an individualistic species. The idea that each person should pursue their own goals and dreams, that they should have their own (public) personal opinions... this isn't unimaginable to them (they have, for several centuries, birthed many human souls) but would be slightly alien or uncomfortable to most.
Therefor, I don't take it to mean that they'd be comfortable with the idea of proportional representation either. Each of the three castes is represented equally at the beginning of the show. Even at its end, the worker caste gains councilors not because it has a higher population, but because it was caught in the crossfire of the factional conflict between the warriors and religious and suffered for it.
The question of whether or not each caste has roughly equal populations is unanswerable, given what we have of canon. We do know that the caste system itself was the mandate of Valen, and so the species and society has only had a few thousand years to adapt to that. There probably aren't yet any evolutionary changes that might help balance populations naturally.