The reason you are having to invest so much time is exactly what you've stated ... "should not have been postponed for so long".
Analogy? Car for which one never changes the oil and filter ... one only adds a can now an then when low. However, can understand users (teachers/students) cannot seem to tolerate much change (which is probably true of most folks in a general sense).
It's just the way it is ... :|
The issue you are having is rather strange.
Think that taking stock of the current 2.2 ... and checking everything ... themes/mods/blocks, settings ... especially addons is in order to anticipate where there might be bumps in the 'march'. Like: an add-on block in the 2.2 for which there is no upgrade when one gets to 2.4 or anything upwards.
And, in the future, reading release notes for each version higher before upgrading so one isn't surprised and put into a 'fix it now' mode. Note: have been guilty of that myself ... got to trusting too much or settled into 'ho-hum - another update'.
'spirit of sharing', Ken