Why do you say this?
Or rather, please educate us on Mikael's game as we know what Markus' is like.
Mikael's biggest strength is his playmaking, especially the way he slows the game down, and lures defensemen closer before dishing excellent passes to his team mates. His problem has been timing on the smaller ice. In AHL he still has time and space on power play, but 5 on 5 game even in AHL was a new kind of challenge for him last season and problems in his 5 on 5 game were the reason he was sent back to AHL during the season.
Markus is kind of the opposite on Mikael. He either passes instantly, or decides to try to push through himself to get to a scoring position. It hinders his playmaking ability somewhat, but it also helps him with the transition to smaller ice game. Markus also has a physical aspect to his game Mikael is lacking. That kind of difference in the state of mind when battling for the puck in corners seems to help Markus in comparison to his brother, as Mikael's best asset in board game is his superior stick work so he will manage if he is in puck possession but is in trouble without the puck.
I'd say Markus also will end up being the better skater of the two, but again, Mikael will be able to handle the puck in full speed better than Markus, I'd think. But all in all, I think Markus already has a similar bust potential as Mikael, Markus really doesn't have to learn all that much to be effective as a goal scoring winger, Mikael has still some adjusting to do before he can be considered NHL calibre center. Hopefully he has been able to do it already this off season, but I wouldn't count on it.