No, i’m not forgetting that. This is a different reason.
Nowadays, Daut also quickwalls and micros (yeah, he does!)…
BUT - the reasoning behind mangonel shells:
If both players micro (one microes mangonels, the other microes archers), the archer player almost always wins even if they are slightly worse at micro than the mangonel player.
If both players micro = both their economies “suffer” - but if they keep producing vills, the economies suffer just a little bit, whereas losing a ton of mangonels is is often a “gg”. Yeah, so is losing archers, but staggered formation and/or micro would still be helpful a lot, but not that much helpful.