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First of all, Contreras defected when he was in his 30s, so he was old his entire MLB career. He wasn't cooked at all when the White Sox acquired him, less than two seasons into his MLB career. In fact, he was an instrumental part in them winning in 2005 and posted consecutive 3+ WAR seasons in '05 and '06 before gracefully finishing off his CWS career as an average starter.
As for your second point, okay? The Yankees had El Duque who obviously was a high profile Cuban player and might've helped them land Contreras. So the White Sox basically took that and ramped it to 11 by acquiring Contreras for the winning run, followed by Alexei Ramirez - who was excellent for them btw - and continued to fill their farm system with Cuban players, with Jose Abreu being one of the highest profile of the IFAs to come to them, which helped signed Robert, probably helped them sign Grandal, and probably helped them sign Yoelqui Cespedes.
The White Sox have a strong history with Cuban players, and certainly Contreras is part of that history, whether he signed with them immediately or not.