I've said before that I don't think that any tag division in the last 20 years has been particulary strong, so I don't think that it's "weakness" needs to be addressed. I absolutely cannot be arsed to get mired down in that debate again though, so I will answer this question as it is.
Mega powers teams aren't really a new thing. Since Raw first went on air and the way wrestling is portrayed changed forever, there have been very few consistent career tag teams. So, the tag division has been almost entirely made up of young debuting wrestlers and haphazard teams that they have nothing to do with.
The former groups are usually split as soon as there is a spot on the singles roster for them, and the latter group generally consist of shite teams that people aren't interested in, with a small amount that click, such as the NAO.
So-called Mega Powers teams have also been fairly consistent since 1993 too. A quick run down oftag champions between, say 1993 and the golden tag year of 2001, gives us teams of main eventers in Yokozuna and Owen Hart, arguably Michaels and Diesel, but they had history, Steve Austin and Shawn Michaels, Steve Austin and Dude Love, Kane and Mankind, Austin and Taker, Rock and Taker, Brothers of Destruction, Two man power trip, Benoit and Jericho and Jericho and Rock. That's a total of 11.
Lets look at betwen 2002 and now, the same number of years. World Tag Team: Kane and RVD, Booker T and RVD, Big Show and Kane, Rated RKO, Cena and Michaels, Cena and Batista, Jericho and Edge/Show. WWE: Angle and Benoit, Batista and Rey,
Which is 10 with 2 titles. So basically, there are four conclusions you can draw from this, take your pick.
1. Tag team wrestling is now much the same as it has always been in the modern era
2. Tag team wrestling is better now, because there are fewer Mega Power teams
3. Tag team wrestling is worse now, because there are fewer Mega Power teams
4. Tag team wrestling is worse now, but it isn't because there are more Mega Power teams.
Take your pick of those, I don't care, but whatever you do take, accept that the prevelance of so called "Mega Powers" teams isn't why the tag division is better or worse than it was before, because there have been a similar number through time, and, if anything, there have been fewer recently.