so split nicely, and for England, Pakistan, Australia, India, New Zealand, West Indies, Sri Lanka and South Africa although I did pull out figures for Bangladesh and Zimbabwe also
2000-2007 (T20is didn't really start until around 2005)
Tests : 658, ave 82. Most = England (103), average without New Zealand (58) = 86
ODIs : 1713, ave 214. Most = India (247), average without England (182) and West Indies (191) = 223
T20is : 83, ave 10. Most = Australia and New Zealand (13)
2008-2015
Tests : 622, ave 78. Most = England (99), average without Pakistan (60) = 80
ODIs : 1465, ave 183. Most = Sri Lanka (224), average without South Africa (151), West Indies (155) and New Zealand (160) = 200
T20is : 533, ave 67. Most = Pakistan (84), average without India (!!, 48) = 69
2016-2023
Tests : 559, ave 70. Most = England (100), average without Pakistan (58) and New Zealand (58) =74
ODIs : 1072, ave 134. Most = India (161), average without New Zealand (125), Pakistan (115) and South Africa (122) =142
T20is : 908, ave 114. Most = India (152), average without England (98), Australia (99) and South Africa (89) =124
*all periods are from Jan to Dec eg Jan 2016 to Dec 2023, although obviously there's time left in 2023.
England : went from 296 to 344 to 333 internationals in the respective time periods, their number of Tests has stayed about even (4 between max and min), ODIs were steady until 2016-2023 so theorists blaming lack of matches might try to explain 2019 (won) vs 2023 (nowhere) .... ODIs for England are down 23.75% from 2008-2015 to 2016-2023, T20is are up 44.1%
For most of the eight T20is are up between 27% (South Africa) and 73% (Sri Lanka and West Indies), the exception(al instance) being India who have more than trebled the number of T20is played, playing 16% more 2016-2023 (152) than next highest (Pakistan 131)
Most of said eight Test sides have remained relatively consistent with Tests played, New Zealand went from 58 to 72 to 58, Australia did dip from 95 to 74 although who knows how much the drops in Tests played is tactical with the farce of point scoring in WTC
You also have to bear in mind whilst ODIs are no doubt more financially viable than Tests you can squeeze more T20is in, less effort/time for your money so most of the shifts are likely, as said already, all about the $$$
It is somewhat baffling re England who could probably field a strong Test, ODI and T20i side simultaneously that they are well below average T20is played - 98 compared to India (152) so at barely 64.5% of India's output and 13.5% below average - even 11% below average if you add in Bangladesh and Zimbawe, the latter (86) does drag the average down more than Bangladesh but playing only 3 less than South Africa
Will ODIs become obsolete? I doubt it, still very much the money there, compare prize funds for the two recent respective World Cups, and very much accessible to the other non-Test playing countries. Tests haven't dropped significantly but are dropping, the numbers played on average were never all that high 82 > 78 > 70. Should also point out consistently across the three time periods England, India and Australia make up 41% to 45% (41.5%, 44.5% and 44.9%) of the Tests played by said eight nations and 40% last two time periods of Tests played by the 'original' 10 Test nations - apart from 2000-2007 when South Africa and West Indies both played 5 more Tests than India (82) they have been 1-3 in terms of most Tests played, and 2016-2023 noone else played more than 68 whilst those three averaged 16 Tests more than that
I should also point out I didn't filter out to include only games inter top 8, so simply, plainly, just ODIs and T20is even if against eg Scotland, Kenya, Canada, Holland etc which does invariably boost shorter format figures but since the figures for respective formats are all internally comparable doesn't matter too much
