Yet they do not imply IRS is operating efficiently, as efficiency is left undefined.
If we're talking about social efficiency, the tax code appears massively inefficient to me. I believe the tax code should be redesigned to reduce that inefficiency. That may obviate many IRS needs for resources.
The IRS budget for 2020 was $11.5bln to support $3.42 trillion in tax receipts, so I'm not sure that's inefficient. Could it be more efficient? Sure, but it's not as bad as people like to paint it. For comparison, the Los Angeles Unified School District budget alone for that same year was $15bln.
But the broader issue seems to be that the IRS is really bad at planning, goal-setting, and managing its development lifecycle [1]. They've burned through $5.9B just on modernization projects since 1998, with very little to show for it. Many of those projects, including replacing IMF and CADE (which was supposed to be the modern system that would replace IMF, but which failed), have been paused indefinitely. Clearly replacing these legacy systems is time-consuming work, but any way you look at it, it should not take 30 years (that's how long it would have taken if they accomplish their current goal of retiring the IMF by 2028).
It's not just that development is slow; this is holding back IRS from operating efficiently. IRS employees reportedly have more than a hundred internal applications they have to be trained in and switch between in order to accomplish basic tasks, and they have a huge backlog.
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.