Avoiding rules bloat is impossible and is going to happen no matter what sort of arbitrary guiding principles are set into place. The argument that scenarios should be kept under a certain tier of complexity so that they aren't nightmares to prepare has its validity but eventually people who GM frequently are going to want some of the new(er) stuff that is available. The problem with any table top RPG is the same that any game by its very nature has.
You have to keep releasing new material in order to keep your player base engaged and active, otherwise your game gets replaced with newer alternatives...or it gets regulated to the nostalgia pile....or becomes that really old game that only a super small but super loyal fan base still even bothers with.
The issue is....
That rules bloat inevitably pushes people away as well. Once a game hits a certain level of options and complexity, it stops being practical on several different levels. This is why newer alternative options draw people towards them. D&D 5th got a number of people back into D&D, not only because it was more of a return to form for Wizards of the Coast but also because the existing top competitors had plenty of time to grow rules bloat and people were getting burnt out.
However, I have heard that several people (at least in my area) have already stopped playing 5th because of a general lack of official options outside of new adventures here and there. (Which kind of highlights that either end of the spectrum comes with negative consequences). Players want new options and GMs want new things to throw at players but at a certain point it all gets to be too much or not enough for just about anyone (super fans excluded). With Pathfinder being an extension of D&D 3.5, there is only so much that can be done before rules bloat is a thing. Even if Paizo only released 2 or 3 pathfinder books a year, that would be 16 or more books since its release in 2009. Things have a natural life cycle.
wither or become a tumor I guess......either way you eventually die