Gzdoom can run voxels too. Here’s a video of voxel enemies, weapons and objects. youtu.be/71AXYp1X_SA
BUT the thing is, there’s so much more than that. Comparing it to build, even with the improvements from ion fury isn’t fair because that’s still fundamentally build. Gzdoom has replaced even physics, movement and hitbox detection. There are so many changes and bugfixes present in the stock doom engine in gzdoom that speedrunners refuse to use it. Speedrunning requires accurate behaviour. But there are other engines for that.
The original doom engine was open sourced pretty early on, and even before that, people were making maps and custom content very soon after release in 93. And maps are being released every day since then. As soon as the source code got out, a bunch of “source ports” aka custom engines started popping up. Some with aim to fix bugs, some to extend the feature set. And because it’s open, the community started to standardize. So most modern ports that focus on compatibility (unlike gzdoom) are compatible with behaviour of multiple other ports. What I mean is this.
Dsda-doom is focused on speedrunning. So it has plenty QOL features for speedrunning, and is compatible with old ports that extended the feature set. Limit-removing is most common, there are hard limits in the stock engine, like number of enemies on screen at once, map size (block size), how many sectors are on screen at once, and many more. Exceeding many of those will straight up crash the game.
Boom is an engine that removes all these limits and also extends the base feature set by adding new trigger actions, enhancing RNG calculations, and much more. That is the second most favourite. Speedrunners love it, and dsda-doom supports it so you don’t need to use the ancient executable. There is dozens if not hundreds of ports, and a lot of those are still in daily use. Thanks to compatibility settings, when somebody makes a new map, they can say “it’s boom compatible” and people get their modern port of choice, run it in boom compatibility mode, and the map/mod runs perfect for everybody.
Gzdoom supports nearly all the ports, and feature sets throughout history, and has plenty extra of its own. Like portals, coloured lighting, advanced scripting with zscript and much more.
That’s what I mean when I say it’s not fair to compare it to build. Doom in one way or another was worked on by the community for 3 decades, build didn’t see nearly as much attention. Gzdoom doesn’t aim to make doom better, it aims to make a good environment for old and new doom-like games. The active communities on doomworld and zdoom forums are in tens of thousands of people. It’s fast more active than many modern games’ communities. It’s a 30 year old game, just let that sink in.
Oh, by the way, there are even people who make content that is vanilla-compatible, which means it would run perfectly on the original DOS executable from 93-94 on a 386 machine.