The "Coin-Flip" problem with games isn't an OverWatch thing...
When I played serious World of Tanks, this also became a problem... where it didn't feel like the game was trying to curate my online experience to ensure I had fun... but instead curate it so as to balance some statistical meta going on in the background... the fallacy of some impossible notion that everyone performs at a predetermined benchmark the same for everyone.
So, eventually it became obvious that the game was obsessed with achieving a global balance in the performance of players and if you are over-performing the game worked to try and cut you down, but if you are under-performing it would build you up.
The comment that whether or not a player should expect to have fun shouldn't be left to a coin-flip of some random match making formula... that reminded me of why I eventually abandoned World of Tanks... too many games were a waste of my time and I had no control over it. The match the system organized was not going to be fun for me and the game didn't care so long as its deterministic criteria was satisfied.
In the early days, watching games end with a blow-out of one team crushing the other was uncommon... then overtime, it became all too common. Like every other game one team is mauled to death in a 15-0 contest.
It all comes down to backend meddling and the constant tweaking and tuning of the formula until a fixed notion of what an ideal outcome should be... (qoutey-fingers) *fair and balanced* game is acheived... but never comes.