Which then leads on to, when was Wlad's prime? Pre being knocked out, or after?

I personally think his style developed into much of what it is now after the losses and he is a far better fighter because of it. So I would say he is in his prime now (Wlad that is)

However, the more cautious approach I think would favour Tyson as he would eventually get through that big long outstretched arm being held in his face.

Pre losses, I think it would have been even easier for Tyson as the defence just wasn't as good as it is now, he was troubled far more often than he ever is now. Quality of opponents maybe?

Vitali slightly different as I don't think he has the fear factor in him still, the guy is yet to be beat (injury & cut stoppage when winning on cards doesn't really count) so doesn't fear being knocked out as much, maybe he learnt from his younger brothers mistakes.