Their defense actually doesn't suck - it's mediocre, and moreover it's very young. Too much youth on D is a definite concern, but that secondary (and to a lesser extent the linebacker corps) is stacked with young early-round talent so it's not like there's not significant room for improvement on defense, and in fact I think it would be unreasonable to expect their defense not to improve as the season goes along and those young players get more experience.
But yeah, if hyperbole is the only language you're able to speak, then sure, the defense sucks.
I thought the Jets were the team to beat in the AFC East before the season. Through 4 weeks, I still thought that, and I definitely still think it now. But stick a fork in the Patriots at your own risk.