1) “assume that the change in incentive doubles the amount of evasion”

I’m not sure this is an extreme assumption. In the US the income tax rates have changed drastically over the last 60 years (from >90% to <40% marginal rate) while the amount of taxes government manages to collect remained roughly constant (~30% of GDP). People do not necessarily do things that are strictly illegal, but they spend a lot of money and effort in searching for loopholes.

3) “immigrants on average contribute significantly more in taxes than they consume in government services”

I can easily believe that statement for countries like Canada or Australia which have highly selective immigration system, but I doubt it’s true for the US or Europe. The study about immigrants in Germany found that all major immigrant communities are net consumers of government resources and most communities remain net consumers even in the second generation. Why would this be different in the US or UK?