Referee Bobby Madden is retiring a year early after growing "frustrated" with the English system.
www.bbc.co.uk
Fairly clear that Madden in part credits a drop in the standard of football as a factor in why he struggled to engage with it. Believe him or not, or argue that he deserved to be at that level - that's still a direct quote when asked why he's retiring early, because the football and the support structures around it were that much worse than he was used to. We know that for a fact, whereas your assumption that Championship football would have been too difficult for him is nothing more than speculation.
As for Gillet - going from doing 4 consecutive A-league grand finals in 40-50k seater stadiums and various internationals to the PL where average attendance is around 40k? That's not a wild step up in scale and he was also almost immediately trusted with PL VAR duties. I don't really believe anyone had any doubts about his ability or fitness and he's clearly proven capable over time - which is why it feels like unnecessary hoops and hurdles. And they're still ongoing because yes, despite being put in SG1 2 years ago, I said 4 years because if you look at his games he's still not getting any real prime appointments.
And does being SG2 plus a PL VAR really give you much more free time than being SG1? And if that really were a concern, why would he accept promotion after 2 years? That's clearly again just baseless speculation.
Random hypothetical referee Dave from Gibraltar has nothing to do with this, at no point did I say we should just throw any FIFA badge referee into Old Trafford. Decisions can be made on a case-by-case basis at this level, but PGMOL/the FA being overly-cautious is actively harmful because it will deter quality referees from making the move they otherwise might. If Szymon Marciniak needed to move to the UK next season, would you make him take the Gillet route?