Diocletian destroyed the economy by continuing inflationary public spending and blaming it on the merchants.

He destroyed any last semblance of the republic, replacing the institutions of the senate with a "Divine Autocracy." Destroying any rights and freedoms the romans still had.

He created proto feudalism by tying plebs to the land, job, and their social class, preventing the social movement that increases economic growth, trade, and wealth in the republic and principate

He created the tetrarchy, a failed system that caused civil war after civil war. When his tetrarchy collapsed, he KILLED Himself in shame!

He is honestly one of the WORST emperors. Almost every single one of his reforms was a failure. During his retirement, called apon to solve the issues he created, he decided his cabbage farm was more important than millions of people.

I wish Emperor Julian was around long enough to revive the principate and reverse his terrible policies.