I think Graham was undoubtably the better defensive coach.
Those figures are deceptive because they don't account for the fact that we're a much better side than we ever were under Graham. Our defence in terms of goals conceded is actually one of the best in the PL right now. But it's the worst in the top 4 and there's the point. We're now comparing ourselves with the best in the country and are found wanting.
Plus the way we concede goals show bad defensive organisation and coaching. We concede far too many from set pieces or long straight balls, situations which a Graham defence would cope with all day.
If we were 1-0 up in a tight game with 10 minutes to go and under the cosh under Graham then you could guarantee that more often than not we'd see it out and win the game.
These days if it's 1-0 with 10 minutes to go then even if we're not under the cosh (and we rarely are these days) there's a constant worry that we'll cock it up. And we do with depressing frequency.
In the Graham days, especially near the end, we were fairly mid-table and our goals conceded was still one of the best in the country. It wasn't pretty but we were pretty tight at the back.
Anyway, the key sentence of my ramble is that we're a much better side now than we ever were under Graham.
And that's because for all his faults, for all the frustrations, Wenger is at a completely different level to Graham as a manager.