Totally agree, all the best players can adapt and unfortunately I don't think he can?
The way I look at it is this - there are a number of professional cricketers who get to the level within domestic first class cricket that they are "performing" - that is to say, they are making a reasonable/above average weight of runs or taking significant numbers of wickets - and there becomes the suggestion that they might conceiveably be good enough for international cricket. Some are sifted out by A Tours, for those countries that have them, others may be the victims of selectorial incompetence/prejudice. The rest eventually get their chance:
A few, the Tendulkars, Warnes, Laras and Pontings of this world are there from day one and never really slip from their perch, always seeming able to keep ahead of attempts to flummox them.
A number fail early doors and slip away as one cap wonders or after thoughts, deservedly or otherwise.
But for most, the step up evidences both their strengths and their weaknesses - be that through the "technical" Kieswetter model of early stunning performances followed by bowlers working out that he couldn't really get in line with the ball to work it around the ground, the "tempramental" one that saw Matt Prior take a break from the England side or the "physical" one that causes James Pattinson, Pat Cummins and Co to miss more tests than they are ever available for. It is at this point that the men are sorted from the boys.
An example of "the men" for you - when Hashim Amla first came into international cricket, it was on the back of some quite significant run scoring feats in South African domestic cricket. He played, if I recall correctly, three tests around the end of 2004 and was quickly evidenced to be vulnerable to his desire to play everything through leg, so he was taken out of the firing line. Two years later he returned with an off side game, improved power and, as can be seen a few years later, the ability to play to a world class level.
This is not to say that Kieswetter is the next Amla or anything like that. It merely evidences how he should have looked at his weaknesses, thought about whether a trigger to help him get in line (when necessary) would help him and worked diligently to develop ways of working the ball around the field between what sometimes resemble wild hacks. That he has not been able to do this, for me, means that he is unable to do it. Game over...