I don't play HOTS, but generally, over time, skill does impact win rates.
Nearly every one of those matches I ended the game with the best stats and still lost horribly.
My favorite though were the team mates that threw at the start of the match or when my team would decide they would rather argue than play the game. Such a toxic experience of a game. Having one amazing match of great fun and teamplay just wasn't worth the 2-5 matches of absolute toxicity.
But overall, it's still possible to have a lot of fun and great matches enough of the time that it is still worth playing.
I'm around low diamond, which is definitely my skill ceiling. It relatively easy for me to assess higher diamonds and masters. It's also easy to asses plat players. Anything below plat looks very similar to me.