I don't think that's how the guidelines are meant to be used. Sure, a British Golden Ale can have some American characteristics, but that doesn't mean that if you substitute all the British characteristics with ones more American in style, you still have a British Golden Ale. I think of the guidelines as an attempt to use words to describe preexisting groups of beer. The fact that those words might also fit something else doesn't mean the two things are the same. There's a jenesequa aspect to it.
Consider this: Soccer is a game played in warm weather on a large grass fields where the goal is to put your ball in the other team's net. The game involves lots of running, passing, and shooting, and is broken into two halfs. Each team has a goalie who stands in the net to block any shot, defensemen who roam around but are generally charged with preventing the other team from scoring, forwards who are supposed to score goals, and midfielders who are sadistic folk that like to run back and forth and do both. Players are not allowed to touch the ball with their hands or to hit each other. Penalties are dolled out with yellow and red cards.
This description fits women's lacrosse perfectly. But women's lacrosse is not soccer.
I haven't had a British golden ale in a while, so honestly, its possible that a session IPA and a British Golden Ale are similar enough to be grouped together. Based on what I do know, that would really surprise me, but I've been wrong before. So at the beer store yesterday I picked up an Old Golden Hen and a Stone Go To IPA. I don't expect them to have many similarities, but I'll let you know if I'm mistaken. Thanks for the excuse to buy more beer!
Too thin or too hoppy for what? Your taste preferences? If you don't like the profile, that's fine. I don't like bud light but I don't deny its right to a category. What should they call the session IPA? You say its too thin or too hoppy to be a "true" APA, and I'd agree. Its a different profile from an APA. Its like an IPA, only lighter, hence the "session" modifier.
Do you mean that there's no BJCP category? Because 1) the BJCP isn't intended to identify every style and sub-style of beer and 2) there isn't a session IPA category, either. Those are supposed to be entered as Specialty IPAs, because they're similar to IPAs, but at the same time, they're not standard IPAs.
Or do you mean that nobody makes a beer that they call an imperial blonde? Ratebeer lists 22 "imperial blondes". There's even an extract kit for an imperial blonde:
https://www.homebrewtalk.com/showthread.php?t=167714