Putting Phoenix at the level of KOS-MOS may be a bit unfounded as Phoenix has further roots within Nintendo itself, and the fan demand has been particularly strong ever since like... the Ballot where Phoenix would place pretty frequently among fan polls. Nothing too incredible but he was there. As N3ON explained though that's not exactly what she meant.
I honestly have to agree with her overall. Phoenix is a character who I would be very happy to see, but his competition is extremely steep. Ace Attorney is a speck on Monster Hunter's radar and Chun-Li is a bigger character than him by just about every quantifiable metric. DMC has cemented itself as one of Capcom's heavy hitters over the last decade as well, while Ace Attorney has been sitting in dormancy for a good chunk of it. So it often comes as a bit jarring to me when Phoenix is listed right among these guys as one of the leaders, but I get why people think that.
Ace Attorney is a notable series and one that would justify its place in Smash very easily, but there's definitely some deep bias within the community toward AA as, like someone said before, an "honorary Nintendo series". This has come to matter less and less over time, as Smash has extended its focus toward all branches of the gaming sphere, but one could argue that Monster Hunter has quite the legacy on Nintendo too. Even Resident Evil, RE Remake was a Nintendo exclusive for years and that was the initial plan with RE4. Ace Attorney was exclusive for a long time, but that deep Nintendo connection isn't really unique to AA either as many Capcom series have rubbed shoulders with Nintendo in significant ways.
Keeping in mind as well that we only have three Capcom characters, one of which was implemented as an echo fighter. So really we have Mega Man and Ryu, with Ken as a bonus. Two Capcom series among a stockpile of iconic and legendary series and characters. I used to think the next spot was anyone's game, but more and more I've come to teeter between Monster Hunter and Chun-Li, the heaviest hitters from a new series and character department respectively. It could be Dante, it could be Phoenix, but those two are quite a bit lower down the totem and Phoenix trails behind Dante a good bit too. I'm not counting him out at all but I'm absolutely not anticipating him either.
As a side note I also have concerns that Nintendo may not see Phoenix as a proper candidate, and by Nintendo I mean traditional corporate Nintendo giving the extremely creative Sakurai orders to develop x or y character. When looking at the Capcom pool, I'd be very impressed if the Nintendo execs went with the lawyer dude over characters who have much more defined fighting experience and history, and more profitable series to boot. This is much more unfounded and I don't want it to sound like I'm questioning his moveset potential, I just don't exactly see Nintendo as being creative with their off the wall picks in the same way that Sakurai is, making Phoenix feel more like a decision that would be made for the base game by Sakurai himself.
Should have saved some of this for his RTC tomorrow, ah well.