Depends on the reasoning for the RS, to decide it "hasn't worked".
The system has given many young / inexperienced Brits opportunities in the top flight, this alone should save money on flights if foreign riders were used at reserve instead.
Also just because a rider hasn't moved out of the RS system, doesn't mean he hasn't improved as a rider. Look at the Championship averages of Jenkins & Edwards, they keep improving - has racing in the Prem helped cause that?
Look at Kemp & Mountain, riders who got dropped not because of poor form but to try & improve the team, this would happen far more without the RS scheme. Maybe that's the only negative I can come up with, as riders like Kemp & Mountain are considered "number 7 quality" so miss out on Premiership team spots.
Even when Dan T got dropped, without the RS scheme, he may not have got picked up by Ipswich, would he have improved so quickly without gaining another spot?
I know some people will say "if you're good enough you'll get a chance anyway" but look at Dan T in the Champ in 2023. No club wanted him at the start of the season, Birmingham signed then dropped him, till he finally got a spot with Plymouth.
This is the sort of thing that could easily happen more often in the Prem without the RS scheme.
Every year there will be riders at the bottom of a teams average (below 4) no matter what system is used, I just think it's better to have Brits in these positions.
I had a quick look at the last season before "rising stars" 2019 to see who ended up at number 7. One promising Aussie (Ryan Douglas), two young Brits (Perks & Sarjeant), three riders who didn't average over the minimum 4.00 (Porsing, Wells, Ostergaard) and one who never returned to ride over here (Berge) so if we got rid of the RS system and ended up back as it was then, is that any better?
Ps sorry for the rambling, I find it hard to condense my thoughts down lol!