I played HoTs for several years up to a bit after Blizzard stopped developing the game (2-3 years ago?). The match maker in that game has always been a hot mess. It was never fun to be given a team of F class heroes while the enemy team had the meta group composition. Even better where the matches were your team would be decent if not for the map you were given. At times it felt like the match maker was intentionally just screwing with you. After blizzard stopped working on the game the player pool shrunk noticeably which amplified the terrible MM problems. I ended up rage quitting the game after playing on average 4 games a night and losing every single one of them for a week straight. Most of the matches were lost at the loading screen due to a variety of reasons. No sense playing a game that just makes you angry.

When playing quickmatch there were certain heroes that you could play and force a win (assuming the map didn't fck you over). For me those heroes were murky and the lost vikings (and usually abathur). My TLV winrate was over 70% because I could just soak and PVE my team to a 2+ level advantage fairly quickly. Murky was a similar experience but I could also assassinate enemy heroes fairly easily.

Sadly those were the only heroes I played that consistently made me feel like I was effecting the outcome of the match. Getting +30 kills as valeera with no deaths and still losing cause you can't get your team to do any objectives is just infuriating..

I don't play HOTS, but generally, over time, skill does impact win rates.