Webber struggled to finish 2nd on a good day never mind a bad one, but that was solely down to him.
If we compare Hamilton's 2014+2015 stats to Vettel's 2011+2013 stats then they have actually achieved very similar results.
Hamilton has 747 points, 30 podium finishes, 21 of them are wins and 18 pole positions with one race left to run.
Vettel had 790 points, 33 podiums, 24 of which are wins plus 24 pole positions.
Vettel achieved slightly more, so unless we assume that Vettel is a significantly stronger driver than Hamilton the only conclusion has to be that the Mercedes and Red Bull are fairly close in how dominant they were. Webber achieved 5 poles and
only a single victory over the same period.
This is also backed up by a certain
mathematical model, which rates the four cars as follows:
2011 Red Bull 8th most dominant car of all time
2015 Mercedes 7th
2013 Red Bull 3rd
2014 Mercedes 2nd
The 2010 and 2012 Red Bulls were clearly not as dominant as this and the 2009 car was arguably not even the fastest on the grid that year, but those three years are the ones Webber was actually closest to Vettel. Likewise Rosberg's best year at Mercedes relative to Hamilton remains 2013.
I think a lot of this is just perception; Vettel had a habit of leaving everyone for dead within the first two laps then maintaining a small gap over his opponents sufficient to cover an undercut, but not much more than that. Mercedes, however, don't do that, they keep that rapid pace up for most of the race so they end up building much bigger gaps to their opponents. This combined with Webber floundering around in the chasing pack makes Red Bull
look less dominant.
I would also disagree that Rosberg is 'completely not a match' for Hamilton, there is simply no way to reconcile that claim with the fact that Rosberg is actually very close to Hamilton in the qualifying and race head-to-head tallies. Those two tallies are binary, they are not affected by car performance.
The points tally is affected by car performance, but Rosberg is about as far behind as you would expect given his qualifying and race result head-to-heads. The one that actually seems to have benefited from the car performance masking their poor form is Webber, who is much closer in points to Vettel than his terrible head-to-head tallies would suggest.
I also cannot think of any other driver that is better than Rosberg besides the 5 I mentioned. I guess Kvyat is the best candidate, but several badly timed mechanical failures on Ricciardo's car has masked the quite large advantage he has had over Kvyat so I'm not all that convinced Kvyat is as good as the likes of Rosberg or Button. Raikkonen and Massa are surely out of the question due to their poor results against Alonso and Vettel, whilst Bottas has had only a small edge over Massa meaning he too is surely below Rosberg. Grosjean was thrashed first by Alonso then Raikkonen for 2 years straight whilst Perez and Hulkenberg have been consistently mediocre despite all the hype, so neither is worth serious consideration. It's still too early to say where this year's rookies lie, and in the case of the Toro Rosso pair it is impossible apart from compared to one another.