I think it was the smart decision at the time though.
We had just signed Ozil, we couldn't carry both in our squad. If only Fabregas had come calling a year earlier, we could've saved ourselves a lot of coin.
Having said that, I don't think he really killed it at Chelsea. He initially played well but he was never an automatic starter, and never managed to become one in the seasons after that. He had his same old problem of not being able to nail down one position. The only time he ever did that in his career was as a no.10 for Arsenal for about 3 seasons.