...I think many of the older fighters & ex-champions-even in their prime wouldn't fair well against the new, more well-rounded, highly trained coached fighters of today. We all know MMA has evolved by leaps & bounds over the years. Bas knows all the tricks of the trade, it's the aggressiveness and improved techniques of today's fighters thats on a different level...
Aggressiveness is probably not on a different level, at least not on a higher one. At Rutten's time, fighters went to a fight to put the oppenent away, today a big part of fighters gameplan to win 2 of 3 rounds. Gameplaning, that's something that really has evolved by leaps & bounds.
And I'm not so sure, whether at HW, apart from the Top5, technique has improved that much. Rutten's striking was technically better than from most of today's HWs. His problem would rather be that he'd be a very small HW today and be overpowered by the big guys.