Absolutely correct. Sometimes, to complete a quest, you just need one more level, and you have to replay many turns, take this skill instead of another, more important one for the game, level up the hero for XP, and complete the quest possibly a week earlier than the opponent. And that's already a strategic advantage on the map. So, you can't categorically state the usefulness or uselessness... We're talking about offline mode.

And yet, I believe that in Heroes 3, despite its balance, the "learning" skill was treated somewhat harshly. The percentage could have been increased. After all, leveling up gives a lot: plus 1 to one of the four skills, plus an improvement to the specialization, plus a secondary skill or its improvement. Together, that's a lot.
As it is, the skill is very specific and is used in isolated cases.