Photons would on average encounter such filaments once in a few million years, over billions of years this is easily enough to adequately give the observed smooth background. Plasma is not transparent to radio waves, so strength should fall off with distance for radio galaxies, this is observed. Big Bang can't explain. This also means the cosmic background is generated locally, not by a distant in time and space 'Big Bang'. Galactic synchrotron processes generate highly directed radio jets.
Quasars show just such features, no assumption of black holes is needed.
Helium abundance results from an early generation of massive stars Spiral arms rotating through plasma produce shock waves concentrating stars, these massive stars explode quickly as supernovae disrupting the shock wave and preventing further massive stars. Cosmic rays from these exploding stars, colliding with plasma, will produce the rare isotopes also observed, no big bang is needed. Gravity at large scales is then so weak that General Relativity effects can be ignored, its predictions irrelevant. Plasma filaments have restricted velocities, the predictions imply a size ratio between objects of one collision distance. This agrees with cosmic density and applies at all sizes from electron to supercluster.