More to the point, they don't own it, they rent it. I don't know what their revenue sharing agreement is with the council, but even if it's good for the club, it's not going to be as good as if they owned the place. West Ham have some of the same issues even though they've got a nice deal. Their 60k stadium takes their overall revenues close to ours, but generates nowhere near the same levels of income the similarly sized Emirates Stadium does (
officially the most lucrative stadium in Europe)
We won't have any issues like that Coventry or West Ham, and neither will Everton. A new stadium will see a substantial revenue increase and that normally leads to better things on the pitch, even if there are exceptions out there that prove the rule.