Then, quite simply, those groups are doing something wrong.
Almost a fortnight ago, I posted screenshots of this boss working absolutely perfectly and me beating it solo, even after I deliberately let the flower pedestals spawn, in your other thread about the same thing…
The boss only gets shielded / becomes immune if you can’t kill the pedestals quickly enough. If that’s happening, it means you / your raid don’t have enough damage. Again, my reply in the other thread shows this is completely functional and could be solo’d.