Hmmm, I dunno. I think Tuqiri was a much bigger loss. He was as strong and powerful as Izzy, had oodles of skill, and was lightning quick.
He's done well coming back 7 years later, but still, we missed out on his best years.
Izzy might've developed into something great, but IMO at this stage he was still just a potential star with some glaring deficiencies in his game that hadn't been worked out yet (defensive positioning, working with support players, draw and pass, speed - not something he could necessarily improve).