If no one demonstrates that a character is good, then a character does not rise. It's not just Isai or Jousuke (who is playing a completely different smash in case anyone here is forgetting,) it's the combination of him + the rest of the other people using said character.
People wouldn't be putting Fox nearly as high if Zenyore and especially LD were not getting that high a placement. People said Fox sucks on Dreamland but then nope these guys did exactly what was needed to put Fox where he probably should be. There are tons of Yoshi mains now getting top 16 if not higher. Thank you Wizzrobe and Tacos for those placements. It's no longer just Sheer and a few others at most.
---- Relation to not 64 below, forgive the "other" intrusion. -----------
I know this is a different smash game but Jigglypuff went from low tier at best to mid and then is now one of the top 8 in melee due to Mango/HBox alone. Jigglypuff was in fact put on top in a super old April Fools list and people could tell it was April Fools due to that placement more than anything.
Peach was bad before Armada. Yoshi was low-tier before aMSa. Sonic/Olimar/ZSS did the same in barlw thanks to their mains.
-----All other smash games aside----
The tier list is a perspective on how characters are doing and eliminating the fact that Isai won the then biggest NTSC-U smash tournament at that point with Jigglypuff of all characters with only dropping 2 games (1 to Dex and 1 to Moyashi) shows that Jiggs has potential. It's not just Isai. I mean he has lost tournaments before and he has lost games. It's not like "hey, my opponent is Isai, therefore I have 0% chance of winning."
And likewise, if a character is losing representation, the character is going down. If a character has no representation, the metagame for said character stagnates. There are barely any good Ness users anymore for example. Most Falcon mains don't primarily use Falcon. Hey, look who dropped.