A real life batman would have a more wiry physique than a hulking one. He'd be more ninja than battering ram.
I think Bruce Lee would actually be a good representation for a more grounded Batman physique.
He also had huge strength without having to look like Lou Ferigno though.
I'm not saying this is how the new Batman should look necessarily but there's nothing about Batman in a more grounded incarnation having to be a huge or "big" guy to be effective.