I don't believe in this statement. A good defence without a good midfield or attack will not win you any title. Arsenal had the best defence in the league last season; they conceded the fewest goals, yet they didn't win any trophies. The same goes for Inter Milan. People always talked about how good they were defensively, yet they didn't win any trophies. Then you look at Liverpool, which conceded goals easily and won the Premier League. Barcelona won every available trophy in pain, yet they conceded a lot of goals.

I'm not saying defence is not important, but if it's good and the attack or midfield is bad, there will be problems.
Arsenal need to focus on its attack. They need a world-class striker and LW. In midfield, too, they need a better CM. Having players that are DMs or double pivot DMs all over the midfield won't change anything.