@AnOminous I'm not saying you are wrong, but its more from my perspective at the moment from looking at a chart that could be what a judge would use in calculating these counts and charges into a sentence.
I'm very well aware of the Sentencing Guidelines. They're not mandatory, but a judge has to justify deviating from them. And actually a judge can dismiss anything unfounded and without probable cause. That isn't going to happen at the arraignment stage, though, other than rarely. Whether consecutive or concurrent (almost certainly concurrent if he somehow does not end up pleading to just one), this is not going to grid out at the high end of even a single potential 10 year sentence.
Even just the involvement of the "managers," who are even bigger sociopaths than Larson himself, and Larson's severe mental issues, are both mitigating factors that would go into a guidelines sentence, even if he were STUPID enough just to plead guilty to everything immediately with no deal whatsoever.
If anything, going after the "managers," as they've done, is likely to turn up exculpatory
Brady evidence that the court has already ruled the prosecution needs to turn over (and risks getting the case dismissed if they do not).

This is pure boilerplate, but why would the prosecution be going out of their way to question members of the "management" that is likely to reveal exculpatory
Brady evidence if they were really intending on hard-charging their way through the case? They actually showed up at the job of one of these assholes. That's not what they do when they just want a friendly chat (not that there is such a thing as a friendly chat with feds).
Also they do NOT add points for just pleading not guilty at an arraignment. That is arrant nonsense. They might if you take it out to a full trial and despite conclusively being proven guilty, you utterly refuse to take responsibility, or if you do something insanely stupid like take a plea deal, then deny your guilt at the plea hearing (Baked Alaska did this once). Not taking responsibility is an aggravating factor, but I defy you to cite me a case where pleading not guilty at an arraignment constituted that.