My max is currently 50, with 0/40 scrolls applied at the Academy. Wiki has this to say:
Tier 2.2 Contains an Improvement for increasing the number of Heroes you can train. 40 levels at one additional Hero every 2 levels.
So... I believe you are correct.
ETA: Of course, that may have changed. Many wiki pages are not up-to-date.
I saw a player raid with 70 Heroes.My max is currently 50, with 0/40 scrolls applied at the Academy. Wiki has this to say:
Tier 2.2 Contains an Improvement for increasing the number of Heroes you can train. 40 levels at one additional Hero every 2 levels.
So... I believe you are correct.
ETA: Of course, that may have changed. Many wiki pages are not up-to-date.