No the point is that if the IRS was at maximum efficiency, more funding wouldn't increase revenues because tax law is tax law: you can't market it or expand the customer base.

But if every new dollar currently produces much more then a dollar in returns, it means it's underfunded because taxes that should be collected, that by legal analysis would be planned for in budgeting, aren't.

And that matters for a great many things, but one reason is that if you pay taxes and want a tax cut then one reason you're not getting it is because actual revenues are lower then they should be due to uncollected taxes.

AKA tax fraud steals from the honest tax payer.