Arsenal are a direct competitor, any price needs to reflect that. We have to make it expensive for them to strengthen, we know they have the money.
Why do a reasonable deal with them which weakens us, strengthens them, leaves us with only enough funds to strengthen a little, but leaves them with enough funds remaining to go out and strengthen even more?
If Arsenal buy him and end the deal not worried that they have overpaid, then we didn't take them for enough.