The point is not if they get a rough deal or not compared to their home income. The point is that the welfare state costs on the tax base won't be spent to their material benefit, so they are not a cost on the state after working lifetime. Forced saving schemes be they state pension, annuity or superannuation are savings which act as investment capital and i am sure sematek and other bodies leverage this, and then in income phase return to the holder but they are not equal to the lifetime cost of care for the elderly, or provision of housing.

Dubai has much more extreme exploitation of low wage migrant labour, not that none of the workforce in Singapore is remittance labour, filipina nannies and the like but I'm not actually talking about construction site labour or the Dubai passport hijack thing.

Must be a fully automated border or something? That kind of commute would be unthinkable between e.g. Canada and the USA for most folks