Dennis, I agree with you 100%. Spar varnish is the best choice for exterior stained wood. However, no matter what you do, exterior stained wood will always be a maintenance issue. The bad news is that it needs to be sanded and revarnished every 2-4 years. The good news is that this is fairly easy to do. If you doubt any of this, just look around the boat yards in the spring. You always find a lot of weekend sailors refinishing the brightwork.
Paint will last a few years longer but exterior wood will always require maintenance. If this were not true, the aluminum and vinyl siding guys would have been out of business years ago. I don't really know for sure but I would guess that painted and faux finished metal or fiberglass doors will require revarnishing on about the same schedule as real wood doors or they might go a year or 2 longer.