should riders be able to buy a seat in MotoGP
How do you stop it? It isn't possible. The teams pretend the sponsors and the riders are not connected, and who are Dorna to say otherwise. Dorna can take control of the issue by sponsoring the riders themselves. I'd like to think Dorna would solve the problem, but in reality, they'd pick under-qualified riders for the same dumb reasons as the sponsors.
Regarding CRT, it isn't a direction to take or not to take. CRT is the result of deregulation and liberalization of the formula, specifically the re-legalization of production parts, which were banned at the inception of MotoGP. At the time, IMS were worried that 990cc MotoGP and 1000cc WSBK would cannibalize one another. No one presumed that IMS were already planning to dismiss the manufacturers and write their own rules, though, in defense of IMS, they had no idea the manufacturers were not going to participate directly and promote.
CRT looks horrible right now b/c there is no one to fill the void of satellite teams. In sociological terms, the plutocrats in the MSMA wiped out the middle class by writing terrible rules, and if not for the responsiveness of Aprilia, CRT would only be a gaggle of underfunded boffins with more ambition than talent. In the interest of being fair, though I don't think the MSMA deserve it, the middle class racing teams were already dead before MotoGP, so the MSMA only killed a group of people that they helped recreate.
If Dorna and the MSMA create a decent formula, the middle teams will become much stronger. New prototype engines will be developed by production manufacturers or by specialty racing companies, and "CRT" will continue to evolve. The bigger the manufacturer base, the bigger the sponsor and technical partner base. The bigger the sponsor base and technical partner base, the bigger the fan base, and the more valuable the B2B network becomes. The sport picks up steam again.