You know something that it depends on the skill of the player and it`s charactier Let`s say that someone is good with Bowser he may possibly be the worse character in the game but since the player is good with him he is maybe the best in the game.(And theamazingman that was long and complicated and I agree with every thing you typed exept the tournament part.)
Well the tier system is there to see that if computers play as these characters, who is theorectically beter, based on stats and running times and hit ratios and all that fun stuff. So obviously it doesnt affect gameplay if there are two humans. The tier system isnt incorect. Its just obsolete.