Historically, it makes plenty of sense. Financial crimes can’t always be solved behind a desk - there was a time when most tax evasion investigations were against gangsters running illegal liquor operations, for example. Al Capone was arrested by treasury agents, not the FBI.
Whether it still makes sense in 2023 is another question that I’d never really thought about until this moment, but my knee jerk reaction is…maybe it does? Hoover taught us what happens when you concentrate too much power in a single law enforcement agency.
In a well-designed government, the IRS would not have any armed agents. If they have an operation where they need armed support, they'd simply call up some other agency (perhaps the FBI, or even local police or SWAT teams) that specializes more in armed agents and operations, and partner with them to conduct the operation. IRS agents don't need to shoot at people; they can let some other highly-trained people do that, and then come in after the bullets have stopped flying and seize documents and analyze them.
I'm not blaming Biden or a boogeyman army. It doesn't make sense at all that a revenue department purchases guns and ammunition. Does your company's accounting department train with weapons and purchase large amounts? Why does the US Government?
Let the IRS do money works, and any of the other armed departments do the shooting, I guess.