While this is the general case, we must remember this clause right at the beginning of the book:In both cases, you take an action to activate the maneuver, and the maneuver specifies what happens next, in some cases triggering another action, but you in fact benefit from one action only.
Specific Beats General
If you see a rule about a specific circumstance which
contradicts a general rule of the game, the specific rule takes
precedence over the general rule. Individual features, spells,
and traits can often “break” the general rule. These specific
instances should be considered exceptions to the general rule.
So the rules allow us to break the general rule of 1 action per round if a feature says so....and Devoted Assault does. We also can look at other maneuvers that specifically limit attacks, such as perfect assault that gives a specific number of attacks and prevents the use of maneuvers that grants extra attacks..... so the rules do have situations where it adds languages to prevent a large number of extra attacks...but this one does not.
The problem with your interpretation, is it requires you to insert rules handling that doesn't exist in the game. You have to add in "restrictions" into the number of attacks allowed, effectively ignoring certain pieces of various maneuvers. My interpretation is just the natural and logical step by step reading of each piece of the maneuver.
Now again if you think that's ridiculously OP I can respect that, but I do think its the superior mechanical reasoning in this case.
Ultimately I think the best version of this to try is.... only the crits given to you by the Devoted Assault maneuver (not the extra attacks granted by the additional maneuvers) can grant you more maneuvers. This is in line with the rules language, while the advantage on attacks and only attacking one target is specified (until the beginning of your next turn), so it does apply to everything you do in the round.....there is nothing that suggests the devoted assault crit benefits "carries over" into other maneuver use.
That is still a very powerful maneuver, but perhaps more in line with what high level fighters are intended to do.