While MQTT is great, I must defend Zigbee: it supports group messaging, which usually also eliminates the "popcorn effect." But that's only part of the story. Most (maybe all? I haven't used a lot but all I have do) Zigbee bulbs support scene clusters, and each bulb remembers it setting for a scene, which can also be recalled with one command. This is what what makes Hue scenes so fast (a recent Bridge update might have changed this, but traditionally, accessories like the Tap and Dimmer have just broadcast this command and the bulbs would immediately respond--they knew what to do--without Bridge communication being necessary) and Hubitat scenes sometimes a bit slow (the hub is emulating this, bless its little heart, with individual commands to each bulb for things like color and level). Theoretically, MQTT could do this too (broadcast a command like "activate scene 28"), but I'm not aware of any bulbs or lighting systems that support this.
In other words, Zigbee handles this quite well, and the "popcorn" effect has nothing to do with the protocol. (It's also not proprietary; it's an IEEE specification. Anyone can make a proprietary profile on top of the standard protocol, but most devices people here use are ZHA 1.2 or Zigbee 3.0 using the standard clusters and whatnot as intended. Z-Wave is a similar story. Wi-Fi is...a mess beyond the fact the protocol itself is standardized, which helps in no way with how people actually use it for devices.)
(Z-Wave might have something similar; I know nothing about Z-Wave bulbs except that color implementation is generally a mess, and I have low hopes for the rest so I'd doubt it.)