Which aircraft has the better armament is arguable. The twin Spandaus of the DV are well placed and the synchronising gear pretty reliable but inevitable slow the rate of fire down. The mixed armament of the SE5 partially overcomes this problem but introduces the rather inconvenient problem of changing Lewis gun drums in mid dog-fight! However, only those wasteful with their bullets or during an uncharacteristically long dog fight would this have been a problem I think.
How would they fair in a dog fight with equally talented pilots and tactics? There would be little worry in the pilots minds of structural failure whilst dogfighting the SE5a but I’m sure the many structural failures of the DV weighed heavy on their pilots minds as did the fact that they were flying an outdated aircraft. I think Richthofen summed it up when he described the DV as ‘…obsolete and … ridiculously inferior..’. Beautiful as she is, she conveys not one advantage save a slightly a better field of view than the SE5a. Normally there is one saving grace allowing survivability if not an advantage to be gained, for instance, the early mark Spitfires could at least out-turn the FW190 if not out-climb or out-run them. But if you neither out-turn, out-climb, out-dive, out-gun nor out-run your opponent the only way to survive is to outnumber them, out-skill them and be very cautious!
