I remember when Dani Alves was slated for his defensive ability. Apart from the beginning of the season just gone he has been the best recovery defender in the world for several years.
What I have come to understand/accept about Walker this year is that, like Alves, it is in his game to be poorly positioned. Such players cannot be expected to be in position at all times, instead they must use their athleticism to a) track back from raids forward and b) to lure the opposition into thinking they can beat them through deliberate 'poor position' before 'recovering' to win the ball.
As with Alves, Walker's physique is certainly up to these tasks, he simply needs to learn a style of defending idiosyncratic to this type of aggressively attacking full-back (very few players fall into this category, with most similar players lacking the physical prerequisites and hence either preferring a wing-back role with more cover structured into the team or as a less attack-minded full-back).
While at Sevilla and even in his first season at Barca he seemed suspect defensively, but by 26/27 he had matured into one of the best players in the world. I'm not saying this will happen for certain with Walker, but with the right coaching he definitely has the potential to become a lethal attacking threat while not exposing us at the back.
When Lennon and Walker were out this season, with Bale playing in the centre/injured we were utter dross due to our lack of width. It seems we are moving to a narrower midfield, or at least one which will require plenty of overlapping from both sides (irrespective of the formation), while Benny is not comfortable hitting the byline, Walker most certainly is. This guy is already a handful for any opposing team, if we give time for him to learn how to make full use of his pace he will cut out the errors and could become one of our key players.
His potential aside, we could not do much better without spending a lot of money. To do so would be pointless on a player of a similar age unless he was ridiculously talented. Even so, we have many other priorities that we could spend such money on including (two) strikers, a central midfielder, a wide-forward and a left-back.
If we could pick up an experienced player to mentor Walker for a couple of million then great, otherwise there is no need to interfere with the development of a promising player (one who, if playing elsewhere, we might all be calling for AVB to sign).