I think the most satisfying Overwatch improvement is when you stop pressing your ultimate the second you get it
For a long time, getting my ult to 100% basically created a timer in my head.
I HAVE ULT. I SHOULD USE ULT.
So I'd spend the next fight desperately looking for the perfect moment, force something mediocre, die halfway through it, and then wonder why it felt useless.
At some point I got much more comfortable just... holding it.
Sometimes the best use of an ult is making the other team play differently because they know you probably have it. Sometimes a normal fight is already won and there is absolutely no reason to dump three ults into the last two people alive.
It sounds painfully obvious now, but learning that "available" doesn't mean "needed immediately" probably improved my games more than learning any fancy mechanic.
What simple Overwatch lesson took you embarrassingly long to actually internalize?