Sky Pillar was quite interesting, in various ways. It was near an island village, which was somehow taken to be connected to significant events and forces, which was a nice touch. The cycling puzzles were somewhat annoying about 10 years ago, and seemed like a slightly strange way of using a cycle - to get over unstable floor tiles and hope not to fall onto the floor below, apparently while still on the bicycle, although the Rayquaza at the top made it totally worth it - and while it did take a few tries, especially since I first encountered it over a decade ago in R/S, it was ultimately quite straightforward to ford it. It raises interesting issues, such as whether it resembles Ted Cruz's potential campaign if they were taken to their logical conclusion as the ultimate Republican. In general, it was a decent route, albeit perhaps too easily reduced to a puzzle stage or area, or in general just a rendered puzzle, rather than an area of itself the way that a few less crowded places in G/S often were.
This sort of seemed to separate it from the rest of the game in some ways. This was also highlighted somewhat by the availability of two bikes, and hence having to potentially get one of those for the Rayquaza thing, etc. It might have also seemed a bit jarring that after facing Steven's Steel-types, Rayquaza was just Flying/Dragon, but presumably Steel/Dragon might have seemed a bit unbalanced, even on a legendary, so they saved that for later. Generally, the air of mystique around these legendaries was decent, in a way, for instance with Rayquaza's location - although the swimmers might seem a bit weird around there, and it is a repetition of Lugia's location in some ways, while you might also have a bit of a grudge against sailing around and so on by then - or the Regis - whose use of braille alongside their appearance in the 'Battle Frontier' might seem humorous - and in general perhaps better than the tendencies in OR/AS and such to crowd these places a bit or not allow you a fairly lonely voyage through Sky Pillar, but it may also come across as a bit of a write-off, or a part of the game consigned to a puzzle segment in lieu of their usual game-play, and in general they did rely on that kind of thing a bit for their legendaries, seemingly not being able to form an organic pathway to them which would convey the atmosphere they were looking for. In that sense they mostly paved the way for the more immediately visible legendaries of future generations, and eventually they had recourse to just finding a location and picking up a legendary from there.