I partially agree, partially disagree... at the beginning, you really have to be content with only the first level (rarely the second), but this doesn't worsen the situation in any way, since most of the time tactical battles are fought with units of ranks 1-3... later, you almost always strive to reach the 4th level immediately... the exception is the Necromancer, who has extremely useful magic even on the third level (raising the dead)...
Usually, by the 4th level, you already have a decent army... but depending on the battles, you use magic from all levels... approximately in this order:
1st level
4th level
2nd level
5th level
3rd level