Testing this in a custom game with unlimited resources in Imperial Age (IV), with some results below. It looks like this might be specific to some technologies - maybe age 3/4?
Research time for Sanctity with n scholars
- 0 Scholars garrisoned - 5m (300s)
- 1 Scholars garrisoned - 4m 25s (465s)
- 2 Scholars garrisoned - 3m 55s (235s)
- 3 Scholars garrisoned - 3m 29s (209s)
… - 25 Scholars garrisoned - 30s
- 26 Scholars garrisoned - 29s
- 27 Scholars garrisoned - 28s (interestingly every scholar over 25 decreases time by 1s)
Research time for Zeal with n scholars
- 0 Scholars garrisoned - 22m 30s
- 1 Scholars garrisoned - 19m 56s
- 2 Scholars garrisoned - 17m 41s
Research time for Boiling Oil with n scholars
- 0 Scholars garrisoned - 5m 0s
- 1 Scholars garrisoned - 5m 38s
- 2 Scholars garrisoned - 6m 21s
- 3 Scholars garrisoned - 7m 9s
It looks like there may be a few techs like this that are reversed (maybe just missing a negative symbol?). My testing in imperial age, it looks like these are the impacted technologies:
- Boiling Oil
- Slow-Burning Defenses
- Village Fortress
Testing with 42 Scholars is hilarious. It looks like these might only be the Keep techs. I started in imperial age w/ max resources - but noticed the same issue popping up in a Skirmish via Hard AI. Noting, with those 42 scholars - research time for boiling oil was >70 minutes, and slow burning was 53+ minutes.