No, neither of them fit the tropes of magical girls or boys.
Adam/He-Man isn't bishounen,
While I might be inclined to agree for original recipe MotU is somewhat on the butch side, the MYP reboot specifically bished up Adam & He-Man as part of the character design brief in an attempt to appeal to that part of the market share. It was one of the criticisms directed at it because the other characters were noticeably more traditionally western in their appearance.
I will however point out that Captain Marvel's appearance was based on the traditional notions of masculine beauty from his originating culture, while Adam's are inspired by the form of the man who won the Mr Universe contest.
the magical part of the magical girl dates to the sixties from Bewitched and similar material, and the transformation is from Cutie Honey in 1973, which is explicitly inspired by a series of Japanese detective films from the early 1940s about a detective who can change his appearances into seven different forms which was inspired by pulps and traditional folklore. His powers are defined, unlike a magical girl's, the plots of the episodes have nothing to do with Adam growing up. The show is also aimed at boys and selling toys, which is a double mark against him having anything to do with the magical girl tropes. Although with the rise of moe and other things a modern show is set to hit both demographics, a magical girl/boy show from the 1980s was most definitely a girls demographic.
You're talking stuff that is essentially window dressing, and ignoring that while the form most people are familiar with might have been refined in Japan, it was effectively invented here in the west, in America, years before -- the country specifically mentioned as creating one of the primary inspiration sources.
It's like arguing that 10 Things I hate About You
isn't essentially just The Taming of the Shrew
because people aren't speaking in iambic pentameter
Nor are MG stories specificially about growing up
-- and here it can be argued that the Aesops delivered at the end of each episode do effectively address such developmental concerns, including on occasion Adam or his friends learning to behave in a more mature and less hot headed fashion -- but rather the wish fulfilment of being grown up
and gaining the agency to address and counter concerns and issues that cannot be dealt with by a child.
Magical girls are descended from Samantha on Bewitched. Transforming magical girls are descended from Cutie Honey who is descend from the earlier magical girls of the 1960s and the Bannai Tarao films of the 1940s.
Which is all well and good, but is ultimately meaningless when they post date the protoform of the trope/genreas represented by the Captain which comes from the end of the 1930s.
He-Man certain has ties to Marvel, which ultimately means he's based on Superman (and considering Adam's mom is and alien and that's part of why he's stronger, faster, etc) since Marvel is a knock off of Superman.
I've always found that idea to be somewhat falacious. Sure they're superstrong guys who can fly, but that's where the resemblance ends. Superman's powers come entirely from within himself and are always active , where as Marvel's and Adam's come from an external sponsor that physically alters them