I think you're being a bit pessimistic Fred, defences need time to grow. Fair enough it was brutal last year but the attributes are there it's just a lack of composure and grit which predominantly emanates from Wenger and his philosophy which makes it difficult for so-called 'tough defenders'.
The centre-back pairing(s) certainly won't digress and Aguero would actually play a big role in a more complete team. He's a Wenger player that's fully formed and no just always on the 'verge'. Arshavin,Chamakh and Bendtner are quite shit in terms of what the other Top 3 have to be fair. Aguero would create situations where less would have to be committed forward by virtue of his sheer quality.
Aguero-fit Van Persie, dear god.