No, they haven’t been vague. They have been very clear on policy.
One-trick is not punishable.
I do think it’s respectful to people to be willing to gel with the team composition, but you can’t ban somebody - it’s not a bannable offence - for just playing one hero, as long as you’re trying your best to win with that hero.
Let’s be clear here and not confuse policy:
One Tricking is not bannable and should not be reported (it even says so in the text)
Not-switching is not reportable
Off-meta is not sabotage and playing poorly is not sabotage.