A molle vest by design has more material than a fixed vest.
Do the math, a fighting load carrier type vest with the pouches sewn on, vs. a Molle one. The vest and the pouches are the same but the Molle version has the loops on the vest and the straps on the pouches. The extra material make it heavier. The pouches also stick out farther as a result of this.
I use both, I have a Platatac, & Eagle fixed vests and a Pantac RAV & plate carrier. I circulate thorugh all four depending on where the game is, what I plan to carry, and what my role that day will be.
Airsoft, where nothing is hurt but feelings.