Clearly a number of factors including the shoes are working together to improve standards. Standards keep getting higher people reset their view on what is good and aim higher each year.
The internet and spread of knowledge of training methods has had a massive impact on standards particularly in the last decade and particularly in younger runners and their coaches. Even before the super shoes the number of sub 4 high school kids was increasing significantly. There are more and more better informed runners and coaches training more and more optimally each year.
There has been a definite increase of people doing more work at anaerobic threshold and running a high volume of easy miles the rest of the time. This has followed on from the work done by Marius Bakken and others posted online and now from the approach taken by Jakob and his brothers. This is a key development as anaerobic threshold is the key limiting factor in endurance running. People did it before but not in such a focused way and not as much of it. The increased polarisation of easy and hard days is equally important.
Sports science has moved on to being more practically useful, more widely available and is continuing to develop all the time. e.g. altitude tents and houses, portable lactate monitors allowing accurate threshold work, strength and conditioning improvements, recovery methods etc.
Better meets with big groups of elite and sub elite athletes of similar standards turning up to run in paced meets for times for qualifying standards or just to run fast. This has particularly been the case through Covid where there were limited races so people turned up ready to go. This has continued as restrictions have been lifted.
Add the shoes and better track surfaces indoors and out to all the above and improvements are even bigger.
I think it is daft to try and put a set time on the improvement from the shoes though. Some people will benefit more than others and if everything else is equal then slower runners will surely get more time as people get a % improvement due to the shoes not a set amount of time per lap or mile.
There should be a lot of credit given to today's generation for training hard, training smart and taking the opportunities to run fast and complete. It's not all the shoes and it is disrespectful to dismiss performances as just down to the shoes. Rojo said in his pod cast today's runners are no better than in the past. Certainly the gap is made to look bigger by the shoes and tracks but some of it is also down to being much better informed than previous generations about training (learning from them and their mistakes) and training much smarter, along with higher expectations or a revised view of what is good. This results in a higher volume of runners at a higher standard from high school, through to college to pro level. More better runners, more chance of some of them running amazing times and more chance of medallists.