"...as was shown with the shoot down of a Turkish F4 Syria had a good air defence infrastructure."
They might have had good AD infrastructure, well even that is doubtful, but given the rings that the IAF ran around the Syrians it was anything but effective. Fast and low fly past of Assad's summer house on the coast, striking PLO camps outside Damascus, taking out the odd nuclear facility (2007 - all open source info)...their IADS wasn't up to much at the best of times let alone now.