If only it were that simple. Full backs - the way we play - are so multi faceted, they are defenders, midfielders and attackers. I think there are incredibly few RB's that do all of those immaculately, and even fewer that are a guaranteed improvement in all aspects, that are available to us.
Why do you think ManU with all their resources have had Valencia and currently have Ashley fucking Young, Chelsea won the league with Moses and now have Azpelecueta (who's definitely better defensively, but not offensively), ManC paid 50m for Walker and recently dropped him because he's been culpable in half the points they've dropped this season (and in the CL) and I'm not the only one that thinks Walker's flawed (
BT Sport pundit Rio Ferdinand brands Kyle Walker a ‘liability at the top level’). But they can't drop him for long because Danilo - the other RB one of the richest club's in Europe bought for 30m - isn't up to much either.
Bellerin at Woolwich - decent but like Trippier, hardly perfect. Liverpool had Clyne and now have a kid (two) they are bringing through (TAA), who's good, but still making defensive mistakes because he's learning, and isn't producing the same offensive output as Trippier.
People talk about Periera, and he's definitely very good going forward, but defensively he's not perfect, made a mistake for one of our goals yesterday, and has cost Leicester other goals with sloppy passing in his own half, and was so iffy defensively in France that Nice played him mostly as a ARM. And what would Leicester want for him after paying 25m for him a few months ago?
Doherty at Wolves seems OK, but they play a much more pragmatic brand of football, would he look as good playing 30 yards further up the pitch with a high line behind him. Trippier averages 58 passes a game at 78%, Doherty, even in Wolves pragmatic system averages 38 at 72%. And he's 27, so one decent injury away from his career being on the downward slope.
Then look at the rest of the league??
There's some kids dotted about, like Atal (who took Pereirra's place at Nice, but again he's only played 7 months of Ligue 1 football, entirely as a WB, so who knows how he'd fair in our system in this league?
WB at Palace looks promising, and you know I think KWP has the potential to be better than Trippier, Aurier and Walker. But that's potential, not battle ready, instant upgrade.
Others may have other prospects they've seen in Spain etc.
If we hadn't wasted 45m in fee and wages on Aurier and just given KWP that game time to develop (lets face it, Aurier's been like a 18yo developing anyway) we might have a solution by now that would have cost us fuck all and peanuts in wages.