I've always thought of it in terms of standard deviation. S tier should be those characters that are 3 SD above average. If you have a 25-35 player roster and 5 of those characters are in "S" tier, it's just not mathematically possible. It's like how 65% of people think they're above average intelligence.S tier is supposed to be reserved for characters who clearly stand out above the rest. That’s how it has been in literally every fighting game ever made.