yes they unironically could have done so much more with vic3, like for example they invented like an engineer pop or something like that, well when you invest in other countries it should have been simulated that like 100 dudes come over for every factory you make or railway or whatever
and then that could cascade into triggering one of those mass-migration events
(i mantain the mass migration mechanic makes SENSE since it kind of worked like that irl, but the general migration mechanics are awful, and the way they implemented the mass migration is also nonsensical like the Bwe'Bwe or BaKongo migrating to Japan because they starved too much.
a proper way would be if there's already pops from that culture (from normal migration) and they have good standards of living, and there's all the typical things that attract immigrants such as free arable land(since arable land is a mechanic), jobs, a decently compatible culture, etc. etc.
the reason 5 million italians went to argentina is because la plata was part of the spanish empire and there was already a decently sized upper class of italian(mostly genoese) traders living there, and from all the connections it cascaded into a mass migration)