Well it's interesting because in some ways, Yvan is right. The pores of the paint can and will absorb solvents and oils from polishing and compounding if the temperature gets up there enough. It's not a big deal when you deal with wax and sealants but it does matter when it comes to coatings. It's why in a lot of ways, a good paint cleansing lotion like the PBL or Mckee 37 paint cleansing lotion is a good idea before a coating if you use an oily polish, it gets worked into the pores and you can pull it out a lot easier, then use a round of eraser or IPA. At the same time while you don't have to use Hyper Polish if you want Glosscoat to last, I do tend to use Hyper Polish, Essence, or Reflect before I coat. I have FG400 but I don't tend to use it unless I'm spot compounding and even then it won't be the final polish as I do find Menzerna to be too oily.
Detailing can get pretty scientific when you encounter certain problems, I don't think it can be helped considering the amount of chemicals we work with. It's like why you can't Eraser and Mckee 37? Because of the lubricating agent in Eraser that doesn't play well with the solvents in M37 Paint Coating. In this instance, to get all the solvent/oils out of the pores would require you to spray down the panel while the panel is at the same temperature as during the polishing process so instead of wiping down after you're done with everything, or use a D/A and apply a paint cleansing lotion like the Mckee or PBL version so you can get the oils out of the contracted pores.
There is no reason other wise Gloss Coat would not last this long, I've seen a few members here who have used Gloss Coat and it lasted two years with decent beading towards the end and that's without any maintenance washes. I think even Corey had it on the roof of one of his cars and left it there for two years without any washes and it was still beading decently after he finally washed and clayed it.