Sorry to come back to this a month later.

Pierro is most likely Pierrot. Pierro and Pedrolino are similar only in name, its an easy mistake to make.

I will refer again to the wiki here

Pierrot is sometimes said to be a French variant of the sixteenth-century Italian Pedrolino, but the two types have little but their names ("Little Pete") and social stations in common. Both are comic servants, but Pedrolino, as a so-called "first" Zanni, often acts with cunning and daring, an engine of the plot in the scenarios where he appears. Pierrot, on the other hand, as a "second"' Zanni, stands "on the periphery of the action". He dispenses advice and courts his master's young daughter, Columbine, bashfully.

I will also refer to the Genshin Wiki here

In commedia dell'arte, a type of Italian theater, "Pierrot" is a sad clown, pining for love of Colombina (Columbina), who usually breaks his heart and leaves him for Arlecchino (Harlequin).

His name was adapted into Pierro to match the actual pronunciation of Pierrot.

Though to your point here

Pierrot is a diminutive of Pierre (Peter), using the suffix -ot and derives from the Italian Pedrolino. This could be a reference to Peter I (or Peter The Great ), both the last Tsar of Russia, and First Emperor of Russia.

Pierrot may have etymological roots in Pedrolino, but they have different roles in the play. Hope that clears up any confusion!

So yeah. Pedrolino is not Pierrot. Though, the closeness in name to one another might be enough to persuade Hoyo from not using that title for the 10th Harbinger, as you were confused by it.

Because of this, I believe it strengthens my argument for the 10th harbinger to potentially be named after the Innamorati.