I get a Tier2 with offensive item in the roulette. I spectate the enemies, buy their champs so they can't get them, go for champs/comps no one else has, get an early 5 interest (around Lv5-6), change a lot in my roster if the draw luck leaves no option (I am quite fast and deftly with it), always have decent combos on the field, manage my items properly. I am rerolling more often than anyone else due to my interest, I am level 8 by the time half of the players are 6. But yet, the enemy has 4 Level 3 Champs in Stage 4, while I have only Lv2's that stand no chance. Even if I get 2 of them level 3, they don't synergize, while I have to fight against 3 buffed Lv3 Assassins every game (I also have 2 Lv2 Assassins but somehow they've drawn theirs anyways), while I can't find a third Lucian to get him Lv2 (Stage 4), with only my 2 Lucians on the field (the 2 Lucians came from the Roulette actually). I have had 10 games in a row now without a single level 3, most of them I got to Top 4 just from unit placement, item usage and a bit of luck in opponent selection (and prediction), but never won.
Also, I seem to have better results with doing none of that and just buying whatever comes in the next rotation, rerolling the whole time and not building any interest. I was in the Top 3 five times in a row, I even got first once. Kind of sucks that the best strategy you can have seems to be not having one because the RNG favors you for it or seomthing.
If the game is not targeting me especially, which I strongly would like to doubt, there must be a better way than "keeping everything observed and playing well", because playing well didn't bring me a single victory or even Lv3 champ.
If there is a good strategy, besides the things I am already doing and assume are the way to go (or should be) - if everyone is following that strategy, it's down to unit placement again. Since I haven't found it (the strategy) yet, it's still down to RNG as it seems. And that way I can just type in "random number generator" on google and compare my outcome with 7 other people and save 40 minutes.