I think theres some differences worth noting about MTTs compared to other variants. In ring games, a basic tight, aggressive style can gradually build up a bankroll. Similarly this style can get you into the money in an SnG, with the time taken being short enough that even if you're not that experienced short-handed you can just get very aggressive, and make it more luck who gets the top 2 places, rather than short-handed playing skill.
Both ring games and SnGs can be profitable mainly playing your cards, rather than your reads on your opponents.
With an MTT, however, being a mediocre, tight player is just not enough. That will maybe get you to the early money placings before you're blinded out, and you'll have played for 2-3 hours for very little money, and no profit once you factor in the times you miss the money. This means sometimes not playing based on your cards but based on position and table psychology.
I suspect that being a significantly profitable MTT player requires the most skill, because you're playing more against better players in the later stages, and must adapt your strategy for the changing feel of the table. One of the skills it does require for the good payouts is short-handed playing skill, so it is useful to have played a number of SnGs first, which will give you more of an idea how play changes on the bubble, and how you need to play short-handed, and once you are getting some firsts in the SnGs and are making a profit, then is probably more the time to consider playing the MTTs.