in my mind, 2s is relevant only to the extent that 2s should be equal to 3s and 4s. so to the extent they are not all equal, then there is a problem.
1s should be greater than or equal to any of 2s, 3s, and 4s (since 2s, 3s, and 4s should all be equal).
while i agree that 4s(=3s) currently is not correct, 5s also is not correct (although 5s is less incorrect than 4s). fundamentally, the observer’s species count (based on “species” from the API’s /observations/observers endpoint) is not correct for you.
the problem is probably related to the the settings on the system’s indexes and the fact that you have so many observations – probably similar but not the same as the issue noted above:
…
UPDATE:
i dug around, and it looks like iNat staff have identified another similar issue before and have chosen not to address it: https://forum.inaturalist.org/t/number-of-species-greater-than-number-of-observation/59789/4. that other issue deals with the observer’s observation counts, but it’s possible that the same analysis applies to the observer’s species counts.