Some teams benefit from absolute control, but it is true that others thrive on being more flexible (particularly for teams with solid players top to bottom). You find absolute control being the most effective at the lower skill levels where you may have some folks who don't really understand what's going on - of course it breaks down if the leader also has no idea what he/she is doing.
The other quote about flanks is almost universal among tank generals in WW2 - the idea was that you would strike first to gain initiative and dictate when and where battles would occur as opposed to being forced to defend again and again, because it was thought that a combination of factors made static defense (which had reigned supreme since ~ the 1850s) untenable. There were also plenty of military thinkers who sought to completely forgo defense entirely, for example the Red Army's field manual prior to WW2 had just over 200 pages on how to execute various types of attack, whereas defensive tactics were reduced to a single chapter, because it was thought any kind of defense was admitting impending strategic defeat .
It's true in TF2 in so far as if you constantly force fights you don't often have to worry about your flank because you'll likely overpower your opposition as long as you can manage to clear the choke and don't encounter a hard wall like an uber - mix^ in the s10-14 era was particularly good at this (that's not to say other teams haven't also been effective with it too - they're just the easiest example) mihaly's flow was built around the concept for the most part. Of course, the counter to such a tactic is strategic depth ;) essentially passive play such that the attack can't succeed in breaking you or turning your own flanks, and as such gets enveloped and destroyed. G.S. Isserson, basically the architect of the Soviet army in ww2 (though he was in prison for the duration of the war) used the word "depth" in virtually every sentence to describe how he envisioned strategic movement lol. In fact for funzies he wrote a book in 1933 called "Deep Operation" which is still classified to this day.