Coding interviews test for fluency. You don't give coding interviews to someone to see how good they are, i.e., variation in speed is fine, you are looking instead for how well they decompose problems, abstract and structure things to make them tractable, and yes, whether coding is second nature to them. People who do extremely well in coding interviews are also going to do extremely well coding with AI. Is the converse true? This is where AI has made things tricky. If the engineer is supposedly experienced and senior, then yes, i.e., if they have not become a good coder by now, something is wrong, and you don't want to bring whatever that is into your project. However, if the engineer is very junior, than not necessarily, they may have chosen to spend their time on more important things than "learning assembly". Therefore, ironically, it is the senior engineers and more experienced folks who you get the best read on by doing coding interviews, but you do still get a good read on them this way.