Beyond whiteboard based coding being a bad medium, on-the-spot programming exercises are a super noisy, poor medium for assessment compared to the alternative: a work sample in the form of a 4-8 hour programming exercise done by the person on their own terms. No exploding deadline, no restrictions on tools other than those necessary to show the person's relevant job skills. Make a bunch of them, put the time into them, and let the candidate have a chance to pick from a library of exercises that are interesting and fun to do.

The main downside to a work sample is that a lot of people will say they simply don't have the time to do it. That's fine, you'll lose some people, but you'll also have people applying who really want to work for the company. From there, you'll have a small number of people who do a great job on it. By the time they are in your office interviewing, the idea that you'd reject them because of a slip-up on a small coding exercise on a whiteboard is absurd, because you already have a mountain of evidence regarding their skills as a programmer. The in-interview exercises will be there to test other skills like communication and collaboration, not writing good programs.