Reading about it now it sure seems to be, and I was completely ignorant of all of it until the last day or two. And I've made my living in computers for 40 years, played computer games, spend a fair amount of time in various on-line places, and watch some gaming commentary. And yet I had no idea. I can't imagine how out of that loop your basic middle class mormon family would be,
...and, subsequently, how out of the loop prosecutors are likely to be. We've had the benefit of an explanation from someone familiar with the culture. And the nuance of it has come as a surprise to most of us here, most of whom are reasonably well educated and attentive. But prosecutors will not care. Gov. Cox will not care. Kash Patel will not care. The case against Robinson will have to be a simple narrative that appeals on the basis of only one or two easily-understood principles. Prosecutors will never try to talk about something as apparently alien and nuanced as gamer culture, even when it would improve the chances of a conviction. The Reagan-era adage, "If you're explaining, you're losing," is a rule of thumb in criminal prosecutions. And it appears those one or two principles are emerging as trans alliance (or trans reliationship) and liberal university indoctrination. I'll bet that the narrative the prosecution will go with is that he was a good, wholesome kid who got radicalized into woke, left-wing politics at Utah State and further radicalized by being in a relationship with a transitioning person—a noted left-wing talking point.
Nor does explaining the nuance really work as a defense. If we suspect that it would work the same way as trying to explain gang culture to juries, that has failed more often than it has succeeded. If the defense brings in expert witnesses on gang culture to explain how threats etc. are not typically to be taken seriously, it rarely lands with the jury. It comes off as a lot of overthought handwaving. If Robinson's defense tries to introduce the gamer- and Groyper-culture background, it may not avail them much.
As I explained above, motive is only partly relevant to the legal case. To charge first-degree murder, you have to show evidence of premeditation, but that can be just as well established by circumstantial evidence as by testimony. The fact that messages of any kind were written on the cartridge casings, for example, is enough to establish premeditation without trying to interpret the sentiment behind them. It doesn't even really matter in the desire to charge aggravated murder, which is the only way in Utah he could receive the death penalty. The acceptable aggravating factors are spelled out in Utah statute. They are numerous and somewhat byzantine, so I won't go into them in this post. But they almost all deal with the circumstances of the crime, not the reasons.
But it's likely that federal charges could be explored. While there's no U.S. Code statute against murder of an ordinary person (i.e., as opposed to an elected official), there are ancillary statutes for things like terrorist acts. For example, federal prosecutors could try to say Robinson was acting on behalf of some group (Antifa, the Democratic party, trans allies, etc.) to commit violence as a means of cowing people.