Yeah, it’s fine. Just know that you’ll occasionally get yelled at if you don’t conform to other peoples’ expectations. That never bothered me as I never much cared about what other people thought. I personally know way more than anyone ever could about my own competencies.
If you don’t mind picking the same thing over and over again, then go for it. Back in the day when Tyrande had so many play style options, I would have had no problems. Nowadays, I’d be bored a lot more easily.
Flex only matters if you’re actually good at the role you’re flexing into. If not, I’d just prefer you play your best heroes. I’d rather play a weird comp well than a standard boring comp poorly. I know that isn’t the prevailing wisdom though.
As a healer main, I like to play other roles sometimes. Some people will offer to flex into healer roles, and if I’m lazy, and don’t check, I might find out later they’re terrible at it and regret it.
Never mistake willingness to cooperate for competency. Those aren’t the same thing.