I think the purpose of not doing that was specifically to keep agency with the main protagonists, just like how Luke doesn’t actually swoop in to save the day as to not overshadow the new characters we’re meant to be following this trilogy.
There’s a way to combine the two, and it’s not an all or nothing, either. I think that, again, simply bringing Palpatine back like that begs the question of old heroes also returning to combat him in this “once and for all the end of everything” type battle. Rey can still have the agency in that situation (coming up with the plan, striking the decisive blow, etc…) but there needs to be the confidence in your own characters and in your storytelling to be able to incorporate these sorts of things into your ending, and if you don’t have that confidence, you probably shouldn’t be pursuing an avenue that actively demands you go there.
It’s just another example of Rise of Skywalker being packed full of scattered and scared decisionmaking. They didn’t have any faith in figuring out how to incorporate past heroes into a generational conclusion so they just sidestepped the whole thing, and it wound up completely unsatisfying. The first thing we see her do in the movie is hover in place pleading for those old heroes to commune with her. The story is itself asking for those heroes to return THROUGH the main character. She’s expressing her agency by asking them to come visit her. If they ACTUALLY VISIT HER in the end, and actively help her strike the decisive blow (or realize the pacifist plan she comes up with) against Palpatine once and for all, that’s not overshadowing her. They just didn’t have the will (or the ability, or the time, or all three) to figure out a way to get to that ending in a satisfying way. So they did a shortcutted half-ass version of it instead and called it a wrap.
Part of the reason Rey is such a strong character in TFA and TLJ is because in those instances, the writers didn’t succumb to the need to protect their character, to remove obstacles from her path or engineer situations so she can more easily realize her potential. If they needed their character to be strong enough to do what the story’s arcs dictated they do, dramatically - they cleverly and creatively wrote their character to BE that strong in organic, natural means within that story. Rise of Skywalker is a good example of writers not believing in their characters fully, and playing “prevent defense” to use a football metaphor.