There is a strong argument that parents are favouring girls if they discipline them more, given lack of rules, boundaries and discipline seems to be a widespread issue.
Also, if the "behavioural standard" relates to sitting still and quiet, then perhaps boys who are more likely to want to be running and shouting and letting out energy and aggression should be held to a lower standard for reasons of fairness - girls can behave 8/10 with ease, whereas the boys struggle to behave 7/10 even when they really try. Why should boys be punished more than girls if the ultimate reason is that the task given is one that girls tend to do better in? (Of course if the instruction was to run around and shout as if you were trying to scare off animals you can hear approaching from the darkness then things would switch and the boys should be held to a higher standard).
I think the main feelings of resentment come from inherently understanding that society, and in particular education, has been feminized in recent decades. And the constant hearing about toxic masculinity, but never hearing about how positive it is that many men can do what most women can't - like carrying people down ladders from burning buildings or step in to stop a violent crime that is taking place. Positive masculinity is rarely celebrated (other than elite level sport which is unattainable), and toxic femininity is rarely mentioned.
Whether or not boys "feelings of resentment" are "valid" and wherever they come from the fact is they exist. I am not sure that dismissing them as invalid helps boys (or girls, or women)