It can be very hard to tell exactly what someone's guitar rig was on a specific recording. Interviews and photographs are the most reliable evidence available. There are sonic signatures to pickups, but they can be overwhelmed by amplifiers, cabinets and effects pedals, particularly overdrives, and recording techniques. For instance Jimmy Page was a dedicated Les Paul player, but it's a Fender Telecaster on many of his early LZ recordings. Go figure.
Mason was a superior guitar player compared to Winwood, but his wasn't a better musician. Winwood clearly has enough chops to be more than interesting.

