What makes diaspora groups such as the Armenians, Jews, etc. so successful? Did the diaspora itself have some marked impact on the culture and trajectories of these groups or is it something else entirely?

A socially marginalised group will not have access to the normal institutional advantages of members of the host society—connections, class privilege, leisure time, cultural familiarity etc. etc. Members of that group will be more highly driven to succeed, to redress those disadvantages.

They will be more strongly motivated to succeed, if they see exemplars of success around them—if some members of the diaspora have already succeeded despite social marginalisation, or if they are intermixed with the host society (not ghettoised), so that they are exposed to paradigms of success from within the host society.

If OTOH they’re ghettoised, and if the diaspora society is insular, so that they are not exposed to paradigms of success—then, not so much. There is less incentive to succeed, if the only experience you have is of failure.

And if the diaspora knows what success looks like, they will use whatever levers the host society does not expressly or implicitly block them from using. Such as public education.

That, btw, is why I did not know any Greeks in Australia doing linguistics when I went to uni. That’s a luxury of established ethnicities. I only started seeing Greeks in linguistics classes when I was lecturing.