Specifically talking about non-new players…I think there’s a balance in the sense that there are good and bad ways to practice.
Something I was taught when I first started programming professionally was to time slot things like brainstorming/theory crafting or testing new things. Both are fine, but at the end of the day I have a job to do and spending too much time on one thing and not succeeding is not helpful to anyone. Go back to it later.
In OW winning never stops being the main objective of the game. Spending some time, preferably near the beginning of the game, experimenting is fine, but after a certain point it starts becoming buttholery if the test/practice is making the overall experience of the team bad. Plenty of other games to do some testing in. No need to completely ruin entire games for four other people before you achieve competency.