A Paladin without javelins or a bow won't help much against a beholder flying around out of reach. A fighter who loses its weapon can't really do anything useful, and they might not shine when the enemy had resistance to damage from nonmagic attacks and the PC had a mundane weapon. A spellcaster without its focus might be crippled. Is there any situation like that where say a sun soul monk becomes bad, or are they more of a "never the best, never the worst" kind of class? I think I prefer being confident that my PC won't run out of obvious good options over being great in some cases but sidelined in other.