I actually took the time to examine DSM's videos (because it is charitable to entertain the whims of the less fortunate every now and then).
https://www.youtube.com/watch?v=9-g8Ywibztg
In this video we see his pet solo killing a seb golem (7500 hp) in approximately 7 minutes. That's 7500hp/420 sec = 17.9 DPS from the pet.
https://www.youtube.com/watch?v=5XwiGKTuu2E
In this video we see DSM spamming a combination of Ice Strike, Canni and Torpor to kill the seb golem in approximately 3m38s. This is 7500hp/218 sec = 34.4 DPS. Note that this is roughly comparable to the DPS a Shaman can put out simply by spamming the JBB (32.9 DPS).
We combine the pet DPS + his nuke DPS to get a total sustined DPS of 52.3 (50.7 using JBB). It's very respectable for a priest, certainly better than what a Cleric or a non-charming Druid could do. But literally no one has ever argued otherwise. But it still falls far short of what a Mage is going to put out, not to mention the fact that DSM is already down to 40% mana after killing a single mob. What's going to happen to his mana bar when he's in a group chain pulling for two hours? He's not going to be able to keep up, and will be reduced to doing exactly what I said would be his best DPS option: clicking /pet attack and spamming his JBB. In other words, performing as a half-rate Mage doing about 50 sustained DPS.
If anyone wants to perform the Lord's work and make a video to shut DSM up: find a 55+ Paladin and a 60 Mage with focused water staff and Boots of Bladecalling. The Paladin equips a non-damage primary (no ripostes). The Mage casts DS on the Paladin and buffs pet. The Paladin pulls the seb golem and holds agro by spamming only blind and stun over and over (zero damage). The Mage attacks with backstabbing water pet and clickie nukes until the seb golem is dead (simulating his group DPS). The mob will be dead shockingly quickly and we'll all have a good laugh as DSM tries to find fault with the math.