Taxes aren't beyond partisan influences though. The UK's Conservative Party cut top rate income tax whilst the budget was in deficit. Clearly, the Labour Party would not have done this. Similarly, the Democrats would not have passed Trump's tax cuts, and the Republicans would not have hiked the top rate
Sure, they are constrained by the art of the possible: massive top-rate rises and cuts are extremely appealing to left/right bases respectively but are constrained by the fact that (i) the median voter they need to woo doesn't like extreme change and (ii) extreme changes usually won't actually have the positive impact on the economy which left/right ideology claims they will. So tax changes usually aren't drastic, and don't show up well in panel data studies. But there's still plenty of changes at the margin and especially to tax incidence which are the result of one party being elected over another.