Trying to think of teams where Markkanen could play a starring role on a contender.
Markkanen would be a nice fit on a team like the Brooklyn Nets as a center replacing Kyrie or Harden as the third star. That is a title caliber team I could see Markkanen playing a starring role on. Durant at PF and Markkanen at C. A creative ball-handler next to them (Harden or Kyrie). Plus some shooters.
I do think Markkanen is difficult to place on a title contender. His offensive game is not well geared to being a 1st or 2nd option because of his lack of both one-on-one scoring & passing / playmaking ability. So more of a 3rd option and most teams do not like defensively deficient centers as their third option. But he could work on that Brooklyn team.
Markkanen would be interesting on the Suns instead of Ayton. Completely different outcome for the Suns. Their offense would be on steroids but they'd lose their defensive base. Not necessarily better (or worse for that matter) but a title contender all the same.
Could also be a 3rd star on the LA Clippers next to Kawhi and PG13. Not a great fit because they have less ball-handling wizardry than CP3 or Harden / Kyrie but it would still be good. I like that ball-handler with Markkanen's PnP game.
He could be a 2nd star (or 3rd star) in Dallas next to Doncic. Then again so could Porzingis if he used properly. That base could form a title contender.
The teams I would be worried about are the ones with star bigs (Giannis, Zion) who are the center of attention and would force Markkanen too much off the ball. I like him near the ball. Around the ball. Engaging the defense.