In my (not at all recent) experience - flying against/with Top Gun and against/with USAF FWS (F-15C course) as instructor, adversary (with 422nd) and friendly forces as well as numerous Flags on Blue and Red, AWC trials, etc - the courses are not strictly comparable.
The 6-month UK QWI course ranges across the spectrum from OCU instructor to mission commander, ie ground-school academic to first radar sortie all the way to tactical and beyond, while Top Gun in my time was a short (6-8 weeks? I forget) scenario-driven, tactics-heavy course - the sexy end. Top Gun was the solely DACT: 1v1, 1v1v1, 2v2, etc, etc on the way up to Balbos of varying sizes and could include work-outs against types that you weren't allowed to have seen. Graduates from the UK course could find themselves on the OCU, Sqn or OEU whereas Top Gun graduates, especially USN, almost exclusively came from and went back to their sqn.
Don't get me wrong, it was very hard work for those involved (and there were some wonderful aviators on both staff and student cohorts), but it was not a pass/fail course and it had nothing like the brutal (OTT?) rigour of the USAF FWS (or indeed the RAF course) where you could fail the brief and be done for the day before dawn and then talk about the debrief of the brief for 10 hours (ah, the sweet memories). There will be those on here who recognize the experience.
As a rule, the USMC used to send its pilots/crews on its combined Weapons and Tactics Instructors course (WTI) first so that they could get the academics and instructional stuff down before going on to the more sexy stuff at Top Gun. WTI wasn't by any means all academic though: missions like 12-ship FLIR/NVG strikes and FastFAC/CAS were also part of it complete with helicopters, C-130s and stuff. In the USMC, you were not considered the equivalent of a QWI or FWS graduate until you had completed both courses. In my view, it was this discipline that made the USMC aviators more rounded instructors (and better briefers and debriefers). And, of course, the USMC guys (no girls in my time) were combined arms trained so could do the A-G thing with the grunts too.
As for the exchanges, the F-18 exchange moved from Beaufort to Kaneohe to El Toro and then to Miramar on the back of software changes, but was concurrent with the East Coast F-14 exchange. In my time, many of the guys from the film were still around and, by then, COs and XOs of fighter squadrons in both the USN and USMC. And, yes, they were very handy in a gunfight.
The career thing was more nuanced. Some of the US exchange officers sent to the UK were distinctly average precisely because of the conscious decision to pass over one's career to go on it. Of course, there were also some very good people who didn't care and came anyway (often on their way to the airlines!), but most of the time people wouldn't swap, say, F-15 for a Tornado F3 and take the risk - and who could blame them?!
Going the other way, the risks were similar, but generally only a slight delay in career progress. And we tended to send people as a bit of a reward, which is why so many of the exchange officers were QWIs. However, even the RAF eventually realized the career risk and started seeking flight commander exchange tours to avoid the need for two sqn ldr flying tours (since exchange officers were often promoted early while in the US). That sped up the process and allowed individuals to compete directly with their peers.
Finally, there was a distinct difference between the flying at Miramar and Fallon in my time. The former was Top Gun, but the latter was fleet readiness so involved the Air Wing turning up and being put through its paces, albeit in a more scripted fashion. I was there when Top Gun was told it was moving to Fallon - the radiant joy was palpable; not sure how many actually moved...
And I have no doubt that everything I've just described is completely different now!