W2 worker is, effectively, a subcontractor to a prime contractor who reimburses all normal work expenses.

I already quoted the IRS webpage where it specifically states that isn't true.

But it doesn't matter. If you are a business and get income from a contract and that contract says "Part of this money includes travel expenses." it doesn't matter to the IRS. As a business, you get income and you have expenses. The details of that income do not matter to the IRS.

For example a business gets $50k of income from a contract that says it includes travel expenses. At the end of the year you actually spent $49k in travel expenses. You report $1k profit to the IRS.

A W2 gets $50k and has to report $50k independent of how much they had to personally spend to get that $50k.