1st of all, I would argue that ROB is a contender for best in the game but that's beside the point. If keeping track of tournament placements is not clear evidence of the viability of characters then what are you left with? Just everyone with their own theories. People can build up any character in their heads; I know at least 2 players who think Ike is "unironically" top tier because he's strong at the locals I attend. When I first started playing smash tournaments in Brawl, I was convinced
was a good character who needed a breakout performance (he's actually bottom tier). Eventually I played good people, informed myself and got over that delusion but what do you say to those people? Why is your opinion more valid than theirs?
Some opinions, like the above, are more farfetched than others so lets focus on the Ike is top tier ones. What would you say to a tournament player who frequently gets top 8 to tell them why Ike isn't? MKLeo won a major with him.
My personal response would be that Leo is an outlier and the meta has developed with better counter play to Ike because I look at trends. Ike doesn't have a trend of top tier performances. People want to win and are naturally drawn to characters who help them achieve this. Ike has not continued to preform at a top tier level. If Ike's good, why isn't he getting top 8 more; why don't top players use him? By identifying trends I can make mostly accurate predictions about the future to a certain margin of error. Smash isn't an exact science; people get banned or lose interest in characters. But I can say with confidence that Roy will outperform Ike at the next major tournament. Maybe he won't, maybe he will. Smash can surprise you. We'll have to wait and see.