Nominal spend is the wrong yardstick when one side builds at home for a fraction of the cost; Russian labour, steel and energy are far cheaper at the point of use, which is why PPP estimates put their real military output roughly level with the whole of Europe combined.
And spend isn't the binding constraint anyway: it's production. A budget line is not a full magazine, and we've spent years throwing our stockpiles into Ukraine while letting our shell and propellant lines wither instead of refilling them.
"We don't need to catch up" assumes the money on the page is already steel in the field. It isn't.