The 5% limit *was* in the ANO, it was removed a couple of years ago. So, now, 21+ members is fine. EASA, so far as I know, has no opinion on the subject. This is entirely a UK concern.
As a serial and parallel share owner, I have embraced this for years and have encouraged many others to also. I think that flying schools griping about it are on a hiding to nothing - but there is nothing to stop them providing services to syndicates such as instruction, hangarage, aircraft management support, maintenance - and some do do that.
G