“Taxation doesn't fund spending; taxation follows spending. This is proven by research.”
In theory yes, it holds true if the spending is for growth, it’s simple logic, invest to provide more income for the future, all businesses do it providing jobs and pay taxes along the way.
Where it falls down is when spending is for social maintenence or improvement, health, education, benefits, environment, etc because the only payback is taxation of income of workers, in the UK there is no product to tax.
For decades in the UK the spending has NOT resulted in even an equal return so our national debt has increased AND the value of sterling has fallen. In the last 20 yrs the National debt has risen from 50% to over 100% of GDP spending has clearly not been rewarded by taxation