I feel unless cuts get extreme she's fine. Kid Icarus may be small, but she's a very popular and important character from it, she's the type of character I'd see them place high on their priority list.
...High priority? Nahhh. No way. Middle priority, I could see the argument, but "high priority" is like, Link or Mario or Inkling Kid or whoever. Characters that you just could not have Smash without. That is not Palutena. I'm not gonna deny her merit but you can easily have a Smash game without her. Pit could have an argument for high priority but not Palutena. There's at least 20 characters you definitely need to include before her.
Kid Icarus is named after Palutena in Japan. In addition, she's majorly popular there(which is why it wasn't hard to see her getting into 4 in the first place).
I doubt she's in any danger, outside of the franchise itself being reduced to 1 character. Dark Pit is easily safe as long as they have time to make him(and even then, he might be planned from the start just like in Ultimate). It's a small series, but that matters little in this context. Both characters are popular in their regions, and the third is hyper easy to make(and popular for other reasons).
I feel like the thing with this argument is, yeah she has merit, but like, so does just about everyone else in Smash. She's popular, yeah, so's many others. That won't necessarily save all of them if they need to trim down.
When you have to decide to split things fairly between dozens of different returning series, I think Kid Icarus being a smaller series is not something that's easy to handwave. Yeah she's an important second character from Kid Icarus... but we have many, many other series, some of which have multiple essentials before the conversation of Kid Icarus's secondary rep even becomes relevant.
I agree Kid Icarus being small wouldn't be a dealbreaker for it keeping
a character, Pit is never leaving, but it keeping its lesser ones is much easier to debate in the trim-down scenario. Once they get as many different first party series repped as they reasonably can and they have time for extras, Palutena's probably gonna be one of the first they look for, but that's quite a lot of ground you gotta pave in first.
(oh yeah you mentioned Pitto. I doubt anything's happening to him but I don't even really count him)