re: swimming world record progression. Rule changes have at times been the biggest force behind record progression. Backstroke had their entire turn rules overhauled 17 or so years ago or so allowing a freestyle type flip turn as opposed to the long standing touch on back and turn rules.
An assault on the records was the immediate result as each turn was sped up multiple tenths of a second.
In the past, rules have been enacted to prevent swimmers from exploiting non technological areas to gain an edge also though. The rule in 88 I think to prevent the Berkoff blastoff in backstroke was actually a rule that limited progression in the world record by restricting the distance one could travel underwater off of walls.
More recently FINA has changed their interpretation of the rules so that the toes of a backstroker may come above the surface of the waterline at the start. This contributes to better starts.
They limited butterfly and freestyle to 15 meters underwater off each wall a decade or so ago- taking away some natural training/capacity edge some swimmers had.
In Breaststroke the downward kick off the start/wall that Kitajima can get away with now historically was against the rules. It has been incorporated into start and turn rules now to streamline the rules for more consistent rulings during races.
So rules in general are changing the standards in every stroke/race and it's clear that some times it contributes towards faster records and some times hampers.
The stroke where rules changes have seemingly had the least impact is freestyle- but you could probably guarantee a new set of world records in freestyle sprints by allowing unrestricted dolphin kicking off walls and it would have more impact than any suit or pool design.
That's not to say that the suits and pool design don't help- obviously they do- but we also have better athletes and training methods now than ever before so it's hard to assign precisely how each factor contributes.
As long as we continue to have races like that relay and performers like Michael Phelps I don't much care.