Secondary skills in Heroes 3.

I wouldn't judge so quickly in your place. You need to consider all game tactics.
1. And it doesn't take more time than leveling up one hero; they just level up in parallel. For example, you level up one hero, and the opponent levels up theirs at the same time. And by leveling up a second hero, you prevent the opponent from leveling up their hero. You can level up the second hero where the opponent's hero was supposed to level up.
2. And is it necessary to give units specifically from the starting castle? There are neutral castles, castles taken from the opponent, and neutral dwellings, after all. Besides, if your first hero is far from your home castle, the second hero can take units and not bring them to the first, but go with them to where the first hero hasn't been yet. Then the map is explored faster.
3. These spells really help to control the situation on the map, but it's not a given that you'll get them. Besides, I want to play Heroes, not "Who finds the portal to the city faster." That is, you need to play according to different scenarios.