I'm not sure how it would change it, the 1% firms number would probably get even more concentrated if you included Microsoft and trading firms like Jane Street (assuming they opted out), but the spend weighted share of VC backed companies would probably go down. However, large VC backed stealth companies may be more likely to opt out. And lots of Microsoft's spend might be on products and support/devops servicing demand from VC backed stuff.

From a recent Dwarkesh interview with Dylan Patel it sounded like Jane Street might be double digits of Anthropic's revenue, but I'm not sure where they sourced that.