Name me two players who could give us what Naismith could, Every player is the sum of his parts, Naismith is undeniably injury prone and as I said wouldn't feature in every game however his experience, nous and will-to-win is something we don't have and that has cost us. Those attributes more than balance out his availability issues plus we wouldn't choose to play him unless plan A was failing. To say he's not the quality required for games in the SPFL is ignoring his performances.
As for you bringing on Kamberi rather than Naismith, that's the kind of thing Gerrard does, isn't it? He brings on Barker or Ojo because he only wants to play a certain way and ignores that they very seldom deliver.
We need steel, Naismith has it. We need to do things differently, Naismith offers that.