The PVC J boxes really do not have a place to provide additional support.
Usually they do just get stuck up on the stubs that come out of the ground. If the pool is built on a stem wall and the equipment is on the ground these can be on some pretty tall pipes. I have never liked it but it is SOP. The other day I had a fellow IAEI inspector say the same rule would allow a transformer if it was made of a suitable material with threaded hubs. I drew the line there. I see you agree with my original contention, that the J boxes were also illegal, although I don't know how else you would do it.
Mine are really supported by the RNC but I have a clamp within an inch of the J box and they are against the wall.