Take the 51 top men's marathon times, 2:04 flat and down, and you'll see that they are virtually all within the last decade. A couple of them are accounted for by the Boston tailwinds in 2011, low 2:03, and others are probably dependent in part on drugs, so that the effect of the shoes could have been muddied by the presence of heavily doped athletes prior to 2016 and the emergence of the shoes on the roads. The only non-aided course results in the list prior to 2016 and the shoes are:
Geb 2008, 2:03:59 (and this was the former 5000m and 10000m wr holder, so the big drop was expected when he moved to the marathon), Kipchoge in 2015 at 2:04:00, Emmanuel Mutai 2013, 2:03:55, and 2014, 2:03:13, Wilson Kipsang in 2015, 2:03:23 and 2013 2:03:42, Dennis Kimetto coming from out of nowhere to run 2:03:45 in 2013 and 2:02:57 in 2014, Patrick Makau, 2:03:38, 2011.
Makau was linked to doping according to multiple articles; Kipsang was banned. So, out of the six 2:04:00 or under marathoners prior to 2016, at least 1/3 were doping.
1 2:00:35 Kelvin Kiptum KEN 02.12.99 1 Chicago 08.10.2023 2 2:01:09 Eliud Kipchoge KEN 05.11.84 1 Berlin 25.09.2022 3 2:01:25 Kelvin Kiptum KEN 02.12.99 1 London 23.04.2023 4 2:01:39 Eliud Kipchoge KEN 05.11.84 1 Berlin 16.09.2018 5 2:01:41 Kenenisa Bekele ETH 13.06.82 1 Berlin 29.09.2019 6 2:01:53 Kelvin Kiptum KEN 02.12.99 1 Valencia 04.12.2022 7 2:02:37 Eliud Kipchoge KEN 05.11.84 1 London 28.04.2019 8 2:02:40 Eliud Kipchoge KEN 05.11.84 1 Tokyo 06.03.2022 9 2:02:42 Eliud Kipchoge KEN 05.11.84 1 Berlin 24.09.2023 10 2:02:48 Birhanu Legesse ETH 09.11.94 2 Berlin 29.09.2019 11 2:02:55 Mosinet Geremew ETH 12.02.92 2 London 28.04.2019 12 2:02:57 Dennis Kimetto KEN 22.04.84 1 Berlin 28.09.2014 12 2:02:57 Titus Ekiru KEN 02.01.92 1 Milano 16.05.2021 14 2:03:00 Evans Chebet KEN 05.03.88 1 Valencia 06.12.2020 14 2:03:00 Gabriel Gerald Geay TAN 10.09.96 2 Valencia 04.12.2022 16 2:03:02a Geoffrey Mutai KEN 07.10.81 1 Boston 18.04.2011 17 2:03:03 Kenenisa Bekele ETH 13.06.82 1 Berlin 25.09.2016 18 2:03:04 Lawrence Cherono KEN 07.08.88 2 Valencia 06.12.2020 19 2:03:05 Eliud Kipchoge KEN 05.11.84 1 London 24.04.2016 20 2:03:06a Moses Mosop KEN 17.07.85 2 Boston 18.04.2011 21 2:03:13 Emmanuel Mutai KEN 12.10.84 2 Berlin 28.09.2014 21 2:03:13 Wilson Kipsang Kiprotich KEN 15.03.82 2 Berlin 25.09.2016 21 2:03:13 Amos Kipruto KEN 16.09.92 2 Tokyo 06.03.2022 21 2:03:13 Vincent Kipkemoi KEN 03.01.99 2 Berlin 24.09.2023 25 2:03:16 Mule Wasihun ETH 20.10.93 3 London 28.04.2019 25 2:03:16 Birhanu Legesse ETH 09.11.94 3 Valencia 06.12.2020 27 2:03:23 Wilson Kipsang Kiprotich KEN 15.03.82 1 Berlin 29.09.2013 28 2:03:24 Tadese Takele ETH 03.08.02 3 Berlin 24.09.2023 29 2:03:29 Alexander Mutiso KEN 10.09.96 3 Valencia 04.12.2022 30 2:03:30 Amos Kipruto KEN 16.09.92 4 Valencia 06.12.2020 31 2:03:32 Eliud Kipchoge KEN 05.11.84 1 Berlin 24.09.2017 32 2:03:34 Getaneh Molla ETH 10.01.94 1 Dubai 25.01.2019 33 2:03:36 Sisay Lemma ETH 12.12.90 3 Berlin 29.09.2019 33 2:03:36 Abdi Bashir BEL 02.10.89 1 Rotterdam 24.10.2021 35 2:03:38 Patrick Makau KEN 02.03.85 1 Berlin 25.09.2011 36 2:03:39 Tamirat Tola ETH 11.08.91 1 Amsterdam 17.10.2021 37 2:03:40 Herpasa Negasa ETH 11.09.93 2 Dubai 25.01.2019 37 2:03:40 Tamirat Tola ETH 11.08.91 4 Valencia 04.12.2022 39 2:03:42 Wilson Kipsang Kiprotich KEN 15.03.82 1 Frankfurt 30.10.2011 40 2:03:45 Dennis Kimetto KEN 22.04.84 1 Chicago 13.10.2013 41 2:03:46 Guye Adola ETH 20.10.90 2 Berlin 24.09.2017 42 2:03:47 Bashir Abdi BEL 10.02.89 1 Rotterdam 16.04.2023 43 2:03:50 Timothy Kiplagat KEN 97 2 Rotterdam 16.04.2023 44 2:03:51 Stanley Biwott KEN 21.04.86 2 London 24.04.2016 44 2:03:51 Kinde Atanaw ETH 15.04.93 1 Valencia 01.12.2019 46 2:03:52 Emmanuel Mutai KEN 12.10.84 2 Chicago 13.10.2013 47 2:03:55 Reuben Kiprop Kipyego KEN 21.08.96 2 Milano 16.05.2021 48 2:03:58 Wilson Kipsang Kiprotich KEN 15.03.82 1 Tokyo 26.02.2017 49 2:03:59 Haile Gebrselassie ETH 18.04.73 1 Berlin 28.09.2008 50 2:04:00 Eliud Kipchoge KEN 05.11.84 1 Berlin 27.09.2015 50 2:04:00 Mosinet Geremew ETH 12.02.92 1 Dubai 26.01.2018