Originally Posted by No Waifu No Laifu

Given the difficulty of obtaining one from gachas, is it better for a rare knight (e.g. rainbow, gold) to get an immediate upgrade instead of being stashed while waiting for copies?

I don't really understand your question. Why do you want to stack up copies first? I can't think of any good reason to. And when you say upgrade, are you talking about raising their levels or evolving them?