The letters don't just mean whatever you want. When you see Top, middle, lower, and bottom, that implies an even distribution of "goodness" amongst each tier. When you say S, A, B, and F, it sounds like S tier characters are way better than A and B tiers, A and B tier characters are evenly matched, and F tier characters can't compete with A or B tiers at all. That obviously isn't the case, and it wasn't reflected in the poll. There was no magnitude of "goodness" being applied to each tier, so to just slap on your own perceptions of how good each tier is relative to the others is misleading. Melee's cast has a very gradual decline. Characters on the edge of S and F could easily be moved into A and B respectively without there being too much disagreement, but the way the tiers are named implies a huge gap between the two tiers. What is so bad about just naming tiers A, B, C, and D? Adding in random S and F tiers comes with all this baggage and misleading connotations for no benefit.