Walcott has one good game in a nothing to play for fixture and everyone raves about him again. Time and time he's shown incapable of playing that well consistently. Added to that the constant injuries and the ongoing argument of saying he's a striker but largely playing on the wing. Once his pace goes, his technique isn't that great and he'll decline quickly.
I think he's an excellent finisher and has great movement but top defenders would easily muscle him out of the game and play him offside. With his back to goal he'd offer nothing. We don't need a striker, we need a wide player capable of taking the opposition on. He quite clearly hasn't performed well in that role for Arsenal on a consistent basis. He can't cross the ball so won't get the best out of Bony and we have Navas to play the exact same role. At 26 he has time to improve but there are much younger and equally as talented players out there.
As for Bony, his record speaks for itself. He has the power and touch of Negredo, a better scoring record (equal to Dzeko) and will put a lot of effort in. Once he settles and forms that partnership with Aguero he'll be a great player for us. It's a big step up and he hasn't quite settled but the summer will give him that opportunity. Strikers generally play their best football around the 26-29 year old period so to have Bony and Aguero in that bracket can only be a good thing. He will also shoot from outside the box, something we've lacked at times.