Against a few players, you have very little edge. I mean if you are a good player. If you are a beginner, a weak player (no offense), the ICM will "work" for you. If there is a ICM. If there is not (winner takes all), this is just, like a cash game. If you are good, you will have a big edge.
The more players is better. Let's say, you double up. You play $5, now your chips is $10, double stack (without ICM). You play against weaker field ($5), they will do the same mistakes (for $5). Also , you "pay rake" for 5$. If you play against more players (MTT), the ICM will be a small factor. At the early stages. This is an edge. "Possible" edge. If you are good...
MTT is very, very profitable. Not like SnG. Not even close...But there is a huge variance. And the big edge not helping much. If you play 3k-4k tournament and you are good, you will have amazing ROI. "Theoretical"...Something like 200-300%. Huge one...But the luck is such a huge factor in this tournament, with many people. And your ROI just don't matters. This is still a "toto", "bingo". "lottery". MTT with 200-500 players is "perfect", but still it comes with a huge variance. Big roll needed...