The diffference is every player you mention, Dawson apart, has well developed techinical abilty. In the case of Dawson, he knows his limitations, whilst Walker does not.
That's partly my point though, there was a point at which Daws was berated for his hoofing and general lack of composure on the ball. Now though, he has shaped his playing style to compensate for his weak areas and I doubt there are many who think he cannot challenge for a first-team place.
Daws is 29 now, Walker is just 23. Just as 6 years ago many who would now see Dawson as a legitimate and proven member of our squad would have judged him inadequate for our ambitions, in 6 years time I am sure Walker will better understand both the weaknesses he cannot improve on, and how to alter his playing style to compensate for them, just as Dawson learnt to do.
To be a serious threat going forwards he does not need exquisite technique. He has the pace to cause anyone problems if he learns to time his runs correctly and interact cohesively with the players down the right flank (RCB, RCM, RW, [R]ST).
Moreover, his delivery is and will continue to improve. Against Chelsea in the FA Cup Semi last year I was in the Chelsea end, my mate (a Chelsea fan, to whom I owe that wonderful experience...) saw Walker raging forwards into space and was terrified, I assured him the cross from deep would be ballooned straight into the stands. It was. We used to have the same problem with Lennon, just like Walker, all he seemed capable of were cutbacks from the byline. By better understanding how to accelerate into enough space to have time to slow down and deliver a more accurate ball, just as Lennon did, Walker's crossing from range will improve.
Nearly every 23 year old full back of this nature has many weaknesses (name me some who have been perceived as world class before the age of 26?). It is up to the management and the player himself to improve upon or limit the effect of these weaknesses. For a full-back, decision making has a lot to do with this, and decision making only improves with experience.
I'm not saying he will become world-class or will even improve significantly, but to write him off now is nothing other than short-sighted.