Surely raw human potential cannot have progressed very much at all in the (at most) two generations represented by the 27 years the record stood.
Granted, the population is significantly higher, so it is more statistically likely that we've produced a genuinely faster human than existed 27 years ago.
I think it's fairly well accepted that most of the records being broken now are down to tech, nutrition, and aids. Springier shoes, mechanical pacers, better 'fuels', deeper understanding of exercise periodization, etc.
Give the old record runner all of the same boosts, the same training, I can't imagine he'd be noticeably slower, perhaps within hundreths, but I'd bet within a tenth or two.
Once that was done the flood gates opened and many others broke it in the following months. This is the “central governor” theory in endurance sports.
We are assuming the old record is "the best a human can do because one person did it best" or some form of that.
There are likely hundreds or thousands of people alive right now who could break this record given the same lifestyle and training.
IMO, better training counts as "raw performance". I think that's more interesting than somebody happening to be born with a genetic advantage.