Nope there has been a drastic change in our defence recently, silly mistakes and bad decisions with positioning weren't present at the start of the season. We didn't look panicked when teams attack whereas now we do, even when under no pressure (e.g. Vermaelan against United).
I can guarantee you he has scored many goals which you, I or any of the other players mentioned could not score. His finishing is generally quite tidy, far far greater than the player you would want to replace him with whose shooting has been appauling for ages now (Arshavin). I actually can't be bothered to break down every point as you are pretty much wrong on all of them.
Firstly, no, Walcott has basically never scored a "great" goal, he is the archetype "standard" finisher. Passes it to the far corner, with the inside of his right foot, or "The Henry", except he's FAR less good at it. The shoot for the far corner, these are standard things, Arshavin very rarely shoots from the positions Walcott does.
Likewise shooting isn't a priority, Arshavin is better ON THE WING which is where Walcott plays currently(not his fault, but he isn't remotely working hard in that position where many many many other players played out of position put in vastly more work). With Arshavin playing we create more chances, and score more goals AS A TEAM, lets not forget that Arshavin scored 10 and assisted 18 in his last full season, last time Walcott came close to those numbers.... never.
Walcott came on just after half time against Utd, did NOTHING, wasn't effective, didn't help the team, didn't score, didn't create chances, didn't defend, did nothing useful in 40 mins or so. Arshavin came on, he created a chance for Giroud, best chance for us to that point, then he in the box faught off Ferdinand won the header, got it directly to Santi, who scored. 10 mins 2 goal chances, one goal scored from them, Walcott 40 mins, no chances, no goals scored himself or from chances, nothing else. Hands up anyone who thinks Walcott would ever back in, hold off Ferdinand then win the header, and get the header directly to an Arsenal player, well I've never seen him do it, or even try.
Teams win off 90 min performances, not a goal and nothing else for the rest of the game. Walcott is rubbish, full stop, Walcott's finishing is not better than Arshavin's, Walcott is not a good finisher. He's a weak shot, he's lazy and he's a joke, if its not an easy chance he basically never scores, if its an easy chance, he scores as often as everyone else. Arshavin 4 goals against a top team, 4 quality goals. Can Arshavin score from 10 yards on the angle, yes, so can Walcott. Can Arshavin score a screamer from 30 yards after, yes, can Walcott, categorically no, can Arshavin get the ball on the half way line, beat two players and score a tap in or screamer, yes, can Walcott, no. Can Arshavin run the ball from the half way line to the goal and set up a goal for someone else, yes, can Walcott, almost never.
On the wing Arshavin is SO much more effective and FAR more productive than Walcott, in the 0.1% of a game either gets played in behind the defence, they are equally likely as each other(and most others) to finish a pretty simple one on one chance with the keeper.
Against Reading, Arshavin took the ball from the half way line, beat players, shot across the keeper in a busy box, and Walcott got a tap in from barely 6 yards... could Walcott do what Arshavin did, no, could anyone on the Arsenal team do what Walcott did, yes.
Compare someone playing on the wing at other top teams, does Mata only focus on scoring, is he ONLY effective when played in behind, do Chelsea look as good when Mata stays away from the ball, and only makes runs in behind and hopes someone else plays him in? Hazard, Oscar even(who I don't rate particularly much). Does any "winger" at a successful club do as little or is as limited as Walcott? Villa's interplay is brilliant, he was an out and out striker, full stop, he's been pushed out wide to suit the team(or Messi), does he ignore every other part of his game? He closes people down, tackles, defends, and his interplay is brilliant. He'll set up other players, score great goals, headers, 30 yard shots, freekicks, 6 yard tap ins. I can't name another player basically in a top league who puts in less work on the wing than Walcott, nor is as poor at crossing, passing, and is as scared to fight for the ball or go shoulder to shoulder. All of them, Villa, Valencia, Young, Arshavin, Gervinho, Moses, all of them can when played in behind one on one with the keeper pass it into the far corner, every last winger I can think of can do what Walcott does, Walcott can't do anything else, every other winger, natural of forced out wide, does more than Walcott.
Again its not his fault Wenger plays him there, but it IS his fault that he puts in less effort, and is less capable in every part of his game than everyone else.