It's looking like they just bald at a slower rate if they have the wrong mix of genes. The tiny amounts of DHT produced in their adrenal glands might be enough to cause receding and thinning at a slow rate, whereas if they had never trooned out they would've been Norwood 7 in their early 20s.
Another possibility is that troons with MPB genes end up getting female pattern baldness instead. TBH it looks like Lucas has FPB because the bald spot is a long streak down the middle of his head. They expect that female hormones will act as some kind of youth elixir, when really, even the ones that passed as hit the wall extremely hard and go back to being obviously trans by their mid 20s (see Bailey Jay, Kim Petras, Jazz Jennings).