Natural Attacks, Multiattack, and Eidolons

I am hoping for some help reconciling a couple of rules. I have an unchained summoner who's about to reach 9th level. Their eidolon has one big slam attack.

# [Natural Attacks](https://www.aonprd.com/UMR.aspx?ItemName=Natural%20Attacks) > Most creatures have natural attacks (attacks made without a weapon). These attacks can be primary or secondary attacks. Primary attacks are made using the creature’s full base attack bonus and add the creature’s full Strength bonus to damage rolls. Secondary attacks are made using the creature’s base attack bonus – 5 and add only 1/2 the creature’s Strength bonus to damage rolls. **If a creature has only one natural attack, it is always made using the creature’s full base attack bonus and adds 1-1/2 times the creature’s Strength bonus to damage rolls. This increase does not apply if the creature has multiple attacks but takes only one.** If a creature has only one type of attack, but has multiple attacks per round, that attack is treated as a primary attack, regardless of its type.

#[Multiattack (Eidolon)](https://www.aonprd.com/ClassDisplay.aspx?ItemName=Eidolon%20\(Unchained\)) > An eidolon gains Multiattack as a bonus feat if it has 3 or more natural attacks and does not already have that feat. **If it does not have the requisite 3 or more natural attacks (or it is reduced to less than 3 attacks), the eidolon instead gains a second attack with one of its natural weapons, albeit at a –5 penalty.** If the eidolon later gains 3 or more natural attacks, it loses this additional attack and instead gains Multiattack.

So, does this mean that a 9th level summoner's eidolon lose 1/3 of their damage potential because they gain a class feature?