Anybody know why I struggle with getting enough blazes to spawn in any% or is it just rng? Like when I go to the spawner only one blaze spawns and then I have to leave the nether and reenter to get another one.

If you wait long enough near the spawner you should get more. Each time there should be 1-4 blazes and a new round comes every 10-20 seconds (I think, I do not know the exact timings.) You may be lucky and find blazes outside of the spawner, although it is more dangerous you should kill them to save time. Yes there is a lot of RNG but if you are waiting much longer than 20 seconds or are only getting 1 blaze at a time maybe you are experiencing a bug of some kind, in which case I do not think I could offer much help but wish you luck finding some.

Thanks