It makes sense as to why they'd be more hesitant on blatant third party shills if you think about it. Third parties obviously require a lot more legal hoops to jump through to get any content from them to begin with which means Nintendo would be more hesitant on picking a character who they couldn't get a decent ROI from as they obviously have to pay licensing and other such royalties which first parties just don't have to go through.
Add on top the fact that Nintendo can't guarantee that the product will be finished by a certain point as they have no control other what other companies do or potential changes in gameplay or writing which could lead to the smash team working on an early build of the character who then misrepresents said character should some giant internal shift exist which means they'd have used resources and time to develop what is ultimately a wrongful interpretation of the character but would likely be forced to go with it anyway which could affect sales for those who just don't like the wrongful portrayal of the character, then yeah.
Hero was just a Hero, not Luminary, but Hero with several protagonists which then meant they could fall back on DQ's own legacy without leaning hardcore into the risky promo side of things. That and 11S was still ultimately based on a game that ultimately existed, so much so, that Sakurai literally said that he was able to base the stage Hero came with off of an already existing version of the game, namely the PS4 one.
I haven't been paying much attention to Nintendo's involvement with SMT, but by virtue of it not being fully under Nintendo, I imagine some of these would still be an issue, even if it's of course significantly less of one than usual. Still, timing screws Nahobino over probably flat out IMO so none of this really needs to deconfirm him when he's flat out not happening.
For the very small yet vocal minority championing Nahobino, a character from a game not even out yet, trying to troll people over a shill isn't going to get people on board at all. Like SMT has a legacy, but why only push Nahobino as the only viable candidate cos of no other reason other than shill and completely ignore other viable candidates who would represent the legacy, be relevant, shill SMT5 just as well and likely be a lot less controversial, who in this case would be Demi-Fiend, but pushing Nahobino with only reason cos of shill and not even acknowledging the series' actual legacy just makes me think that someone has caught that the smash fans hate blatant promo, case in point byleth, and thought they'd troll with a similarly recent character, which, as said previosly, is kinda petty as its trolling.