"It isn't killing us to hold $130bn of bills at 5%+".

Not killing, but still a slow loss of blood.
T-bills have averaged 5.16%/year rate in the last 6 months.
A half year of that would be pretax interest of 2.58%.
After 21% corporate tax, that's 2.04%.
Inflation has been 3.00% in the same six months (not annualized).
Real after tax return on T-bills in six months -0.96%
Annual real after-tax rate of return -1.91%/year
Agreed, that is certainly way better than substantial inflation and no interest.
But it's not better than no inflation and no interest.

As an aside, it's good to remember that elephants can also be funded in part with debt, not just cash.
One of the things that Berkshire has quietly done with the annoyingly large cash flow in recent years is to reduce consolidated leverage.
Debt is lower these days than historically normal levels. For example, head office would have to borrow over 30% of book value to get the leverage to where it averaged around 2016-2017.
[Total assets : Shareholders equity] ratio averaged 2.23 from early 2016 to late 2017, and was never under 2.15 in the prior 3 years. It was 1.929 at end of Q2.
That "unused borrowing power" amounts to over $110bn (one AT&T or Mondelez), without touching the cash pile, and bringing leverage only up to the old normal.
Counting spare cash, there are only about 25 US-domiciled firms that could be ruled out as prey purely on size.

Jim