I actually disagree with you on this nuze. It's all very well saying that teams should just improve whilst playing aggressively in an attempt to break se7en's playstyle but if teams have the objective of winning then it's far easier for them to play passively than play aggressively.
With the amount of incentive there is in TF2 and time that players are willing and able to put into the game of course they will attempt to take the path of least resistance to win. All teams that have contested (and even beaten) se7en have resorted to playing more slowly even if they don't do so vs other teams. Froyo and EVL games vs Se7en at rewind were significantly slower than games vs one another because both teams were taking fewer risks. This is pretty much the definition of a meta.
Even in much larger games, teams will play a style that has been demonstrated to be effective and although they might have differing styles, you won't see many teams playing in a way that goes entirely against conventional wisdom.
I think it's completely fine to alter the ruleset or gamemode to create a shift in meta. You see this done all the time in other games, large and small by developers. Valve only significantly updates the game once or twice a year but we do have the tools as a community to change things and then go back on them quickly if they prove to be catastrophic. The meta has shifted since 2014 to what we have currently exactly because of both valve and community based updates to our balance and gamemode.
5cp as a gamemode had an extremely good flow to it in the past and I think the entire current state of TF2 is a testament to what happens if you don't have frequent balance changes tailored towards creating a new way for people to play a format.