I must admit I haven't tried the build because it requires a lot of setup (like other testers, server hosting, lag and replicating scenario's). It would be hard to make a fair side by side comparison. I think for a lot of players the 'faster packet build' is more easy to understand. It also helps that there is a video that explains the side by side comparison.

Hot take: Most players are vocal about lag when in reality it's just their frustration. If there's lag then it's often not as onesided as believed.

A connection delay between players is inevitable, it's just about whoever gets to be right about what visually happens: The shooter, the server or the victim. I'm confident that shifting the dynamic will just be controversial anyway. Players can think they benefit from a different setting until they are experiencing being on the worse end. I like the way it currently is, because the server deciding is a nice 'middle ground'.

I feel like the public test build is pointless and not something worth pursuing. Before testing I think it's better to question if there is reason to change something in the first place (and opening up a discussion that is a big can of worms). The fact that some players are frustrated seems a bit too flimsy as a reason to release a test build to me.

Players will always be frustrated (read: passionate) about the game. I'm sure that the server deciding what happens also benefits those same players in some ways, but that's not what players remember. I think even after collecting enough feedback a change will be too controversial to put through regardless.

Here's my experience from other games: I've played a P2P online game called Awesomenauts for many years where the shooter decides what happens (for damage calculation). This was not always fair due to the laggy players knowing their weaknesses in their connection and thus start adapting to a playstyle that works best for them. One of the things they do is go for swift strikes (playing like an assassin). Normally players have a very short time to react and retaliate to this playstyle, but with laggy players they now couldn't because of the damage already applying to them before it happens. Similarly, there's crowd effects in the game that work the opposite way (calculated from the victim), such as an area snare. You could never catch someone laggy in it.

In short: Shifting it will keep players unhappy. With >300ms games can be very frustrating and unfair. But that will always be the case.