(And by the way I realize in a lot of companies, 'architect' is a completely bogus term for someone who's more of a flim-flam man than actual doer. So just substitute "staff engineer" or whatever you call it.)
But the main parts of my job I have to get right are picking the right approaches technology-wise, and setting up frameworks and patterns to make devs' lives easier in building out the actual features. You can't test that stuff on a whiteboard imo. You have to just talk it through and try to get a sense of how the potential architect/lead thinks about problems.
It also takes a good architect to interview an architect imo. There's plenty of great devs who just haven't acquired that level of scope yet - not of thinking not just about how easily it is for you to get something done - but how easily it will be to maintain as a team, within the greater ecosystem, over the life of the product.
