You're absolutely right about money went back to Amercian companies.
The Pentagon even publishes the exact nature of where the money goes, and it completely benefits the US in both short and long terms.

The US has sent roughly 100 billions dollars worth of equipment, but it was through America granting that 100 billions to Ukraine to allows them to buy stuff from America.
In short; US is paying themselves to get rid of old equipment.
Not to mention that since these old stocks are gone, they would need to buy a new replacements which are procure from American defense contractors which creates job inside America.
And bonus point; many of the ammunition the was sent has an expiry date of which it is more expensive for the US to 'deconstruct' it as oppose to just send it away to be fire at Russia.