Webb showed glimpses this year that he's still got it. That means he hasn't lost his ability, rather his motivation was the main issue.
http://www.nrl.com/telstrapremiership/gameanalyservideo/tabid/10910/default.aspx
The above link shows a few of Webb's moments:
Round 7 (vs Parra)
7:15 (good acceleration with draw and pass)
Round 14 (vs Canberra)
33:00 (power and balance as he makes a break in heavy traffic, though throws a Mateo-esque pass at the end)
Round 16 (vs Cronulla)
39:40 (runs a good line, making a nice bust for a try right on halftime)
Roun 22 (vs Brisbane)
78:50 (shows more than any of our halves this year with a quality flat ball before the line)
So as I said, they're only a few moments but they show what he still can do. I think Kearney's the kind of bloke who can get Webb switched on week-to-week, and while he'll probably never hit the kind of form he was showing in 2007, I'm sure he'll still be first grade quality. Especially as he'll be in the front-row where all he'll have to do is run the ball and tackle people coming straight at him.
If he's had any weaknesses in the last few years it's been his fitness and lateral defence - these can be hidden better at prop than in the back-row. And his speed and power are still top notch.