It should not be a major surprise that the gap between the haves and the have-nots will widen if you have a large compareable influx of have-nots, or to speak more precisely, an influx of new citizens with low social-economic status compared to those who already were ctiziens. In a very dispassionate perspective, it is just plain math. It is going to take time to return back to the same levels as before.
Oddly enough, profitability of Swedish banks has been increasing for the last 14 years: https://www.macrotrends.net/countries/SWE/sweden/net-migrati....
Maybe you can come up with an argument actually grounded in reality, rather than the same old BS "oh it's the poor".