I'm a bit confused by your statement:
"Even with modern Power Supply SRS units we can still see the poor RF quality from the receivers"
What effect would an SRS unit have on received signal quality (or lack thereof) from a receiver?
BTW, there is no guarantee that a 900MHz receiver will not have similar issues to what you have observed on the 2.4GHz band.
Even when I flew 53MHz 'back in the day', I would still have to be aware of any nearby 6m ham operators.
IMHO, the Weatronic system had a very good antenna; much better than Jeti's simple coax antenna. Of course you could add an external antenna to Jeti (warranty and regulations aside).
FWIW, I always assumed that Europe was just as regulated with regards to spectrum as the US (via the FCC); at least that has been my experience.