Remember that matchmaking (both the publicly displayed skill rating and the hidden MMR attached to skill rating) is merely a number is that is for the most part based on your ability to win and lose matches. Now some matches feel like instant wins… and instant losses and I think you are looking to have matches that feel like you had to play hard to earn each win. Overwatch at all ranks rarely goes that way (and disparity is even seen in pro play like Overwatch League).
Source: RE: WHAT’S THE DEAL WITH MMR - Old Forum Archives
There is a very in-depth topic that is kept up to date that answers most questions.
Post codes if you see fit. However to save time let me remind you that the one common factor that contributes to each of those matches always will be yourself. I recommend using the replay tool to figure out where you have made individual mistakes and how you can correct them. This can include why and how did you die each time, did you play the correct heroes, was your positioning good to be able to secure kills or heal your teammates? All of these questions and more must be constantly re-evaluated every time you play if you are interested in seriously climbing.