Ewing's Jane Foster book had an entity cite the Five's resurrection as a reason why death has no meaning, alongside the Green Door. Page. Legitimate resurrection through cloned bodies is also possible (See: Nick Spencer's Spider-Man.) The fact that cradles weren't shown as any less valid than the Waiting Room, and that no writer or story in the past 5 years contradicted this beyond the copy problem, show that in-universe, the Resurrection Protocols are legit.
As for the clone problem? We don't know. It's an exception that was largely avoided outside of Beast, Laura and one of Maggot's maggots. They just never explored the implications and if the clones are simply clones, or if they share a soul with their original selves, or if one has a soul and not the other, or what. But their unique cases don't mean that all resurrections are fake.
As for these characters themselves, I like to think the clones are also legit. I mean, why can't two people both be aspects of the real person? This is a world where we have beings who prefer to be part of a hive mind, Jean and the Phoenix may or may not be one and the same, gestalt beings exist, people can go back in time and live alongside their past selves without issue, and Franklin has split into different aspects of himself. Yeah, those are pretty different from cloning, but it's a world where such things could very easily be possible. But this part is just my theorizing, not anything that's been proven in canon.