The tightness around the thighs is just due to how low they go compared to women's underwear. I love my boxer briefs. Of course, since I am in Japan and men have way cuter underpants than women I have ended up with enough to provide an army with crotch support 😀 Boxers were too loose for me and rode up my legs all the time, and I hate-hate-hate tightie whities, but boxer briefs are perfect. Speaking if which, I had to throw a pair out... Time to go back to the store...
Edit to add: the tightness lessens the more you wear them, unless they are spandex or Lycra.