So 172 driver, with some expenses taken into account we are talking about 2000-2200€ average per month during the second year at the company (for contractor cadets).
If we say that actually only 11 months are paid (because of the unpaid holiday period) this is the same: 2180 - 2400€ per month (11 months) + 1 month unpaid.
It becomes obvious that the most favourable strategy is to remain based in Ireland where the employer SS is 0%, thus increasing by a 33% the income with respect to Spain.
Numbers are even worse in other countries where the SS taxes are higher and the cost of living is higher as well.