To answer your question with a question - Would you be satisfied if they could solve the problem in that setting? Is making a laptop available to them for problem solving that much trouble?
Or, rather than looking for _any_ competent candidate, are you looking for someone like you and your coworkers, who can give direct answers without a pause? I ask because in one case it's more like an attempt to hire capable employees and the other is perhaps a subconscious attempt to maintain a monoculture.
You know that's a good question and, to be honest, if they could only solve this at a keyboard then I wouldn't be satisfied.
We constantly draw things out and scribble over it again when we're designing. If you can't translate and communicate to others then it's not a good fit for me.
Or, rather than looking for _any_ competent candidate, are you looking for someone like you and your coworkers, who can give direct answers without a pause? I ask because in one case it's more like an attempt to hire capable employees and the other is perhaps a subconscious attempt to maintain a monoculture.