Good morning!
When it comes to Smash speculation, and "upgrades", it's not a black and white situation all around. Based on experience since Wii U/3DS back when I was a wee youngin' in his freshman year of college to start, much of Smash speculation comes back to popularity as the "most important aspect". However, there seems to be a discrepancy between base game and DLC characters. There's also the fact that when suggestions are made that largely don't suggest what many consider an "ideal outcome" those suggestions aren't taken seriously.
This in itself is, from my viewpoint, based on the fact that there are two different conversations happening usually at the same time. Some folks are discussing (and sometimes arguing) which characters are "likely" based on given scenarios, and I don't believe that discussion should be discounted or given the characterization of "confirmation bias" as that's not always the case. The other discussion happening is folks who want to talk about the characters they want to see in Smash. There's nothing inherently wrong with that, as that's why most folks come here to post.
The thing is though, those conversations don't really mesh well together. If I say a particular character doesn't seem likely based on X, Y, or Z, the fans of that character more times than not will come out in defense of that character, when the goal wasn't to defame a character, but to measure/discuss potential inclusion.