My response: Frankly, I have no idea, not even one and so I 'investigated' and this is what I found this from Mr. Hussain:
Al I. Husain, Pretending to be Lester Bangs without the BangsU
It’s a great question and hard to answer as from general observations, Ronnie has filled in quite well as the nice guy of the group with well-groomed guitar chops to handle any material Keith sends his way.
Wood is the youngest and least associated with the group as he joined the band circa 1976 for the Black and Blue album which was well after the Stones golden years that ran from Beggar’s Banquet in 1968 to Goats Head Soup in 1973. The Jimmy Miller produced albums were the Stones at their finest with the prodigious Mick Taylor playing the lead guitarist role. Once Miller and Taylor both departed (or asked out), the Stones were never say the same, taking on a second relapse, the first being the removal and death of Brian Jones and then the resignation of Mick Taylor. In retrospect the Stones may have always known their best days was behind them and settled on finding someone that could provide stability instead of inspiration. That’s not to say Wood’s ability to play is not up to par. He is an excellent guitarist as well as utility player who played rhythm guitar, lap steel, pedal steel, bass and of course, lead guitar. Afterall, he was the mighty six string engine for the underrated Faces and was not green to playing in a globally recognized band.
But their wasn’t anything significantly critical to Wood’s impact with the Stones. He did co-write several songs for the Stones on future albums, but the contributions were paltry. In some ways, its arguable that any accomplished, well versed guitarist could have filled the lead guitarist role for the Stones by 1976 and it would have been adequate. To reiterate Ronnie brings stability to the Stones within the context of being in a wild rock band. 43 years later he is now the 4th longest tenured Stone and still doing what he does best. Taking that for what its worth there is merit in his contribution where the value of it comes from his virtuous professionalism.