No, it's not unicorns and rainbows. My argument does not rely on the existence of such ceteris paribus firms, my argument is that this will affect decisions to invest on the margin. Maybe right now, the margin is deciding between a great company in the US versus a crap company in Ireland, but the one in Ireland looks more attractive due to tax reasons. This policy change would push it back in the right direction. The point is that because there is a margin somewhere, it must be shifted by these policy decisions.

I don't see myself relying on strong assumptions. I am laying out some simplified models to explain the core mechanisms of what's going on.