Actually, I've given that some thought before. Since by default you would assume a fighting games tier list encounters imbalance in a way that forms a normal distribution, depth would be maximized by banning every character past the 60th percentile or so, since it maximizes the number of characters close to the quality of your best character. So mid tier tournaments are optimal.
That's never ever going to happen, though.
Strong Bad's point is decent enough. A tier does cumulatively make a large amount of money, and 66% of something else qualifies as "comparable" for me. A tier is more than one character but it's still a small number of characters compared to the cast as a whole. When his point forces you to move across to "well, MK doesn't have counters, A tier does", you've sort of admitted that the money argument isn't working so you need to theorycraft to show why MK meets ban criteria.