In this case, I agree with you, but as I understood it, Ley suggested specifically creating an army of 7 units from different castles (all 7th level, 6th level, etc.).

Not quite, or rather, not at all. I didn't suggest it, but rather tested the strength of individual 6th-level units one-on-one, through battles lasting several turns. That is, first, for example, Nagas fought against Psychics, then against Wyverns, and so on. Groups of monsters of 1000, 100, 10, and 1.

Ley, with negative morale, my units often skip a turn, but positive morale is much less effective (twice or even three times less).

So what? And have you never had a monster move twice in one game turn? And regarding the fact that "+" is less frequent - I can't agree - they have the same probability of occurring, but in the game, "-" can occur 10 times in a row, unfortunately, it happens sometimes :(

The Ifrit's shield doesn't count as magic (I don't know why) and works even on dragons. And its power, if I remember correctly, doesn't depend on anything at all - it's a constant value and doesn't depend on the hero.

This value isn't entirely constant - it depends on the number of Ifrits themselves - I think you'll agree with that?