Yeah I found RtDL's single player pretty lacking too. It certainly had a strong spectacle for a first playthrough, but when it came to repeat playthroughs it felt like every area was designed around one or two abilities, and if you weren't using those it was like the game was side-eying you going "Hey, uh, buddy, this is the part where you use the FIRE ability. Y'know, the ability where you shoot FIRE? The one we gave you at the start of the section? Hey, hey, how about you use that FIRE ability already?" Basically every Kirby game has a few moments like that, usually for something like Wheel where the level really NEEDS to be designed in a specific way for it to be effective, but it felt like the whole game was designed that way. Its not something I'd experienced in a Kirby game before, and thankfully I never experienced it in Triple Deluxe or Planet Robobot, so hopefully this new game won't have that feel either.
Return to Dreamland left a very bad taste in my mouth for a lot of reasons, but this probably has to be highlight. The spirit of Kirby is that the series gives players freedom to experiment how they want to complete the levels, but this design was sidetracked in RTDL in favor of spectacle. Nowhere is this more apparent than in the super abilities themselves -- you're clearly expected to waltz through those parts of the levels with broken super powers and clear challenges meant only for that ability, and if you choose not to take it then you just have to awkwardly maneuver around obstacles that you can't interact with. It's so boring.
The bulk of the game felt really hand-holdy in general. Ability pedestals are everywhere, enemies pose no threat, and even the challenge sections rubber band itself so the wall almost never crushes you. While Triple Deluxe and Robobot were also very easy games, Robobot at least was more open-ended in its levels (even the armor itself is way smarter in design than past "super ability" iterations).
As for Kirby Switch, pretty excited. It really does look like a revival of Kirby GCN -- they decided they wanted to try 3 helpers again, so they added move combos so they could design levels and puzzle rooms built around the coop element. Smart move. If the AI's decent enough this should still be really fun in single player.