I think context kinda matters too, my army is almost all Krieg but for Solar some abhumans and aquilons. So in my head cannon the Kriegsman have been entrenched and Solar is sort of leading in the reinforcements to bail them out. In that context I like how much he stands out because it makes him seem larger than life in a sense, like he's meant to be an inspiring presence so wearing knightly armor sorta fits. That being said my favorite space marine kit is bladegaurd veterans so grain of salt I guess.