"Homeland Security" is a umbrella grouping of organizations that were independent pre-9/11 and who were combined after 9/11. Seemed like a good idea, at the time!8-))
When you're arrested you're arrested by someone from a particular agency: a Secret Service agent, a member of the U.S. Customs and Border Protection, the Federal Protective Service, the USDA, INS, etc. Creation of DHS "merely" brought 22 agencies under one umbrella for coordination. Of course, judgments and plans made in haste often age poorly.
I'm not saying DHS is a good thing but there's a better explanation than the alarmist "HS was destined to become a secret police force." See
"Break Up the Department of Homeland Security":
https://slate.com/news-and-politics/2020/07/department-homel...
And remember Hanlon's Razor:
"Never attribute to malice that which is adequately explained by incompetence."