Your main issue is that you're looking to Reading Festival to show you new rock music. Look to festivals like Arctangent and 2000 Trees.
Once again, for anyone complaining that there's nothing new or different, I promise you that it's because you're not looking hard enough.
Reading festival has pretty much always been a pop cross-over festival, which is fine, if there has been rock bands, that act will have had a wider appeal for one reason or another.
With regards to Bring Me The Horizon, never been a fan, but go and listen to Count Your Blessings and Suicide Season if you want rockier Bring Me.
I also go back to this feeling of if someone accuses a band or artist of 'selling out' or (in the case of rock/metal music) writing lighter music in order to succeed etc, then that person obviously has no real interest or understanding in creating art. If they did, they would understand that someones artistic output changes and evolves over time.
Some artists might subscribe to this idea of creating to a formula exclusively to be popular, however I would offer that they are the exception rather than the rule.
Si