I think you are reversing causality here. No doubt the EU could have seen similar numbers of refugees from Syria and Iraq and Afghanistan, had they allowed them in.
Before the current crisis, there were >1M Ukrainian workers in Poland, hundreds of thousands in Slovakia, Czechia, etc. The world where Polish, Slovak or Baltic people watch dying Ukrainians through their border fences was never going to exist. The possibility only ever existed in the minds of some confused Americans and maybe western Europeans. German policy in the previous refugee crisis (especially with regard to non-Syrian migrants) literally made the present course the only possible one -- something along the lines of "If we are letting random Africans in, how can we not let the Ukrainians in." is hard to argue with.
On the other hand, accepting even less refugees in the previous crisis is something that was definitely (politically) possible at the time.
