KK - Anybody that has cycled in a group will know how much energy you can save by drafting. No matter how strong a rider is, he won't leave 3/4 slightly weaker riders working together.
To add to what others have said, even if energy is being saved in a pack, if it's moving fast there'll be some working hard to stay in it while better riders are finding it easier. Elite triathlon isn't simply about who is the best runner, it's about minimising the energy used swimming & cycling so that you can run 10k as close to your 'fresh' 10k pace as possible, but at the same time working sufficiently hard to be in the front group and keep it quick enough that your rivals are not going to be able to run as quickly as you. There's a lot more to the bike leg than simply pootling around in a big group, although I would agree that it doesn't make for great viewing.
There may well be some in the field who could beat the Brownlees in a straight 10k race, but they're not able to run to that potential in a triathlon because they're working harder on the other legs. There's a young American guy at one of the world cup races who had the second fastest run on the day, but he hadn't been able to keep up with the lead group on the bike and ended up down the field, although he made up a lot of places on the run.