I think Mark is taking that into consideration. It is expected that one's form would dip if the performance of the car is lacking or if the driver has trouble adjusting to a new configuration. This happened to Alonso in the same period and to Lewis at Merc in 2009. So I don't think Mark would find it an acceptable excuse for purposes of his rating these drivers.
Overall, a very good post, just to pick you up on something here.
Lewis in 2009, is not comparable to Seb of 2012 in terms of adapting. Seb was being outperformed on a few weekends by Webber at the start of 2012 (Silverstone and Monaco for example) Lewis in 2009 was not really troubled by Heikki, from what I recall (a quick scan reveals he finished behind him in China) I would say Lewis adapted better in 2009 than Seb did in 2013.
Now, I suspect you might have meant a typo and meant 2013 and not 2009? If so, I still think the adaption phase for Lewis was much worse (not that I am defending him, which I will get to in a moment) Lewis had a entire new team. Plus Webber had the same circumstances and at least in qualifying adapted better than Seb at the start of 2012.
However, Lewis at the start of 2013 struggled relative to his teammate a lot worse than Seb did in 2012 in my opinion, so I am not out to defend Lewis or anything.
I find it hard to excuse a driver for not adapting. Look how Prost took like a duck to water at Ferrari in 1990, how much Schumi extracted from that dog of a Ferrari in 1996 (first year in the team, and maybe his best season in a bloody hard to drive car by all sources), or how much Senna got from the Williams in 1994 (3 poles, and in the first race he was a lap ahead of his teammate, who was firmly established already at Williams)
I am not holding it against Seb as such, as I am sure he will adapt later in his career to a change in situation, he is too dedicated not to. But in 2012, he did find difficult at first. 2013 he was right on it though, the results in comparison to Webber early on with the tyre problems confirm that.