Considering how vettel has been the last couple of years I would probably say that Red Bull he won titles in was as dominant.
RBR had their strengths & their weaknesses, with there being times where no matter who the driver, they would've lost to better cars on the day. Then look at races from last 3 years in comparison, & note in first 2014-2015 they won 16 out of 19 races. This year they have won 19 out of 21 races.
Sure, you probably don't like Vettel, but can you at least be objective about something like this which rarely happens? Mercedes is perhaps as dominant as Williams/ McLaren from their better days. Heck, even Ferrari's 6 on the trot with Schumacher weren't this dominant. In one of their most dominant years, they did one amazing race at MagnyCours, where they stopped 4 times to beat Alonso who stopped thrice. Mind, this wasn't the only time where they pipped an opponent on strategy, but is one glaring example of such which is hard to miss. They almost always had to push even in their best years (2002 & 2004).
This is not even a complaint about Mercedes' dominance. I'm slightly puzzled/ dismayed (a bit of both), that while Mercedes should have had broken that MP4/4's record, they didn't. I'm saying Mercedes should have won more, and i'd have liked to see that happening given the car.