Learn Farsi: این پیکره بزرگ‌ترین همه است.

Usually, a superlative adjective like بزرگ‌ترین (largest) comes right before the noun it describes without an Ezafe, like in بزرگ‌ترین پیکره (the largest sculpture). However, when we want to say the largest OF a group (a partitive construction), we treat the superlative like a noun and connect it to the group using an Ezafe. Here, the hidden Ezafe connects بزرگ‌ترین to همه (all), giving us بزرگ‌ترین همه (the largest of all).

Could I use the preposition از (from/of) instead of the Ezafe here?

Yes, you can. Saying بزرگ‌ترین از همه is completely natural and very common, especially in spoken Farsi. The Ezafe construction used in this sentence is slightly more literary and concise, but both mean exactly the same thing.

If I wanted to say the largest of the sculptures, would the Ezafe construction work the same way?

Exactly. You would just replace همه (all) with the plural noun. So, the largest of the sculptures becomes بزرگ‌ترین پیکره‌ها (bozorg-tarin-e peykareh-ha). The Ezafe simply links the superlative to whatever specific group you are singling the object out from.

I usually see مجسمه used for statue or sculpture. How is پیکره different?

While مجسمه is the most common everyday word for any statue or sculpture, پیکره comes from the root for body or form (پیکر). It often carries a slightly more artistic, formal, or monumental tone, usually referring to a large figure of a person or animal.