This claim is not correct in several ways. The $80B was not earmarked for hiring agents; that was an additional $80B for the entire agency spread over 10 years. While some of that money might be used to hire additional agents, it will also be used to upgrade old technology (the IRS still uses software from the 1950s), make fixed capital investments that have been long-deferred, regulate third-party tax preparers, provide better customer service, crack down on tax evasion and improve enforcement.

Additionally, this funding needs to be set in the context of an agency whose budget has shrank 20% over the last decade and whose staffing is set to further shrink through attrition and retirements. The IRS Commissioner testified that the IRS would have to hire 52,000 employees over the next 10 years just to keep staffing at current levels [1].

Finally, the Treasury has argued that this $80B investment would (conservatively) lead to an additional $700B in tax revenue over the next decade, so this spending ends up being entirely revenue-positive [2].

[1] https://www.irs.gov/newsroom/written-testimony-of-charles-p-...

[2] https://home.treasury.gov/system/files/136/The-American-Fami...

Edit: since this is Hacker News, I thought it worth pointing out that most of the IRS' software is written in COBOL. I can't think of many things more inefficient and cost-ineffective than continually making bit-part upgrades to 60-year-old software written in a language almost no one knows anymore because of a lack of predictable (human and financial) resources needed to rewrite it.