There's definitely something to be said for prior MOBA or MMO PVP knowledge being a big thing for getting a leg up in this game IMO. As the game plays very similarly like a mish-mash of both via the way skills are used and the style of objectives, it makes it easier to adapt once you see each map and hero in action.
I wouldn't worry about the tier lists so much. The higher you go the more it can benefit you (by eeking out an extra bit making victory easier), but starting out and just playing in general you can play literally just about anything if you can create a competent build.
You should be able to quickly identify (in < ~5-10 games) whether a hero is right for you and you can succeed with it or not, or at the least whether you can succeed with it after more practice.
If I had a caution for playing new heroes it would be simply be "pay attention". Upload your games to hotslogs or keep track on pen and paper - if you're rocking a 33% winrate after a bunch of games on that hero do some research and figure out why. Maybe your build is wrong, maybe the hero is combo oriented and you aren't landing it, etc etc. It's kind of a disservice to your own game experience and your team if you don't make any effort to change or improve if you're set on playing that one hero.
MMR stuff only gets tracked post-30, right? i'm still a long ways away from that, i think.
And yeah, @jon bones, your MMR was being tracked from the first game you played in QM. If you're at ~50-100 games played in QM already, you are already narrowing pretty quickly on your bracket.
Im not sure if it's really so significant or easy to get stuck somewhere, but i havent experienced it so i cant really speak on it
I would argue that you do know how easy it is to get stuck somewhere. If I look at your hotdogs, you were ~3700 within your first 50-75 games. Basically a full year later you are still ~3700. At a few points you climbed ~200-300 MMR and got in the 3900's but have since fallen back and at one point fell to ~3500 but climbed back. That's just basically backing up what folks are saying. It's hard to go beyond your MMR threshold without a shit-ton of games.
We've seen from the Blizzard MMR charts that Hotdogs is actually pretty accurate with the placements (ie: you belong in Master or Platinum or wherever), just not the order of players on the Hotdogs leaderboard since players only need to play like 5 or 10 games across two months to remain on hotdogs leaderboard whereas with Blizzard's monthly chart they must play 50 games EACH month, so I feel pretty confident saying that it mirrors the system decently enough to be considered.