Russia is on verge of bankruptcy. Average Greek has much better life that average Russian.
China have even bigger structural problems: corruption, aging population, empty cities, lack of own technology, weak retirement system, bad education etc.
This choice about Brexit will impact mostly economic situation. If UK vote for Brexit people will start losing jobs.
Brexit is therefore a choice between political elites. A remote, unseen, neoliberal, corrupt political elite or a closer, familiar, neoliberal, corrupt political elite.
Presenting this as a choice of economic self-interest is irrational.