The whole problem with that argument is stacks are never going to be efficient for very much of a match at the competitive level unless there are actually no counters, in which case obviously something broke anyway. If there are counters to a stack, you can have (fewer) of your team switch to the counter, destroying their stack. The stacking team then has to swap AGAIN or else just get rolled over. Since stacking requires more players than countering, the stacking team is going to have way fewer ultimates in the matchup, which are game-changing abilities. If you're giving the enemy team 3-4 more ultimates (or more) by trying to buy (inherently limited) time with stacking, at the competitive level, you're going to lose.
It doesn't have to be perfectly balanced. It just needs to keep following the rock-paper-scissors system and have meaningful, impactful, ultimates.