I'd still prefer 'tomboy' over transboy or whatever, but it's daft pretending they're a breed apart. They're just girls doing things all girls should have the chance to do.
"Tomboys" are girls, and the term is sexist (if all the fun stuff is always framed as boys stuff, it certainly encourages internalised misogyny)
However, it would be disingenuous to say that "action girls" are 100% identical to "girly girls". They are very different personality traits, with very different interests, which often persist into adulthood.
The same could be said of other traits, e.g. some boys are remarkably sensitive and artistic, some children are bookish, others are not, some children are highly sociable, others are not...
Human personality traits are very diverse (and several traits can be combined within the same individual), and they tend to persist over someone's life. We don't have to accept these traits as gendered. But we should certainly recognise and celebrate them, not erase them by saying "everybody can and should enjoy exactly the same things"