Rough Roman Memes

That was definitely one of the bigger motivations. Splitting units into unsustainably small sizes (typically about a fifth of what the largely self-sufficient legions were) and centralizing production of military equipment both, theoretically, reduced the potential of generals to independently marshal support and start a civil war. Unfortunately for this theory, this resulted simply in the high-ranking members of the Imperial family who were commanding ad hoc armies to do literally exactly the same thing despite the smaller formal unit sizes.

Other structural military reforms, like the multi-tiered system of troop quality, the focus on border defence, and lifelong conscription + automatic conscription of soldiers' sons had other motivations. Cost was a big one. Godlike majesty doesn't pay for itself, after all.

To be more fair to Diocletian, as much as I hate being fair to Diocletian, the Empire at the time was hardly in excellent straits, and while I think most of Diocletian's choices are dogshit, the idea that something needed to change to maintain the Empire's stability was far from absurd.

... but economics are not a type of cheese, caste systems are not a solution to anything, getting worshipped as a god is peak megalomania (regardless of how 'traditional' the eastern half of the Empire found it), making the Empire's military systems brittle to save your own skin gives neither imperial protection nor imperial job security, and holy shit FOUR Emperors? How did that ever sound like a good idea?

At least he didn't fuck the coinage like every other shit Emperor, and some of the good ones too.