I looked into that, that pincer op was canceled regardless of the situation in the Balkans, IIRC before the operation was planned due to concerns about being able to cross the Dniester, which led to the delayed 11th army operation and Romanian army mobilization.
Yes, I'm aware of the concern of crossing the Pruth river. As was Creveld, which however indicates that that was a convenient excuse for cancelling the operation in the immediate aftermath of Lustre.
Whether Creveld is correct or not is debatable - but I thought it worth mentioning that he actually does claim that the Balkan campaign had a significant effect on the execution of Barbarossa - although not on the timing of the attack (which he says couldnt start before the start of June).