Life is very fair so I don't think u can blame your landlord. If the situation reverses, like during economic recession ore building renovation, some tenants ask for a rent cut during 生約.
As for asking for a rent cut during free rates concession period by the govt, if the opposite happens and the govt raises rates, can the landlord ask for more rent fr the tenant? No, the landloard has to absorb any loss! So how come the tenant should benefit from a rates cut.