Walrein is not a good special wall. Hello Thunderbolt and Focus Blast Weakness! Hello no useful resistances outside of Ice and maybe Fire! In other words Walrein just doesn't cut it. It is a special wall, it just isn't a very good one. Oh, did I mention Grass Knot will OHKO it from anything with decent special attack?
Bronzong is pretty challenged itself at special walling. No weaknesses and tons of resistances helps, but not resisting things like ghost, dark, fire, bug, and especially water work against it. For example, Starmie will 3HKO it with STAB surf, which isn't even supereffective and Starmie's special attack is very very average for a special sweeper.
As in, if you run in to something like sims' Nasty Plot Raichu, both of your "special walls" are going to die. Remember that (besides sims :P) nobody even uses Raichu in OUs, just imagine what more powerful OU pokemon like Infernape, Roserade, Zapdos, Azelf, and Gengar will do :0
So they really aren't GOOD special walls, sorry.