In practice the tier 1 has the tech and know-how to convince the tier 2 to remain cooperative against their own interests. See the contemporary US where the inequality is rather high, and yet the tier 2 population is impressively protective of the rights of the tier 1. The theory that if the tier 2 has it way worse than today, that will change, remains to be proven. Persecutions against the immigrants are also rather lightweight today, so there is definitely space to ramp them up to pacify the tier 2.