But of an absurd post this one. The fact that they run less than others and older players can play at CB takes nothing away from the position. The reason for this is pretty simple, ones pace is the first physical attribute to fade with age and CB's do not require pace. This is also why CM's such as pirlo play until 34 etc. Titles are won and lost on good defences. Recently, English clubs have really struggled in the Champions league. This has coincided with English clubs spending the majority of their budgets on exciting attacking players rather than top defensive players. Look at the summer for example. Which club spent upwards of £70m on defensive players? Chelsea. Which club is going to win the title this year? Chelsea. In conclusion: Yes, they are important.
I agree with your conclusion, however I'll add that titles are won and lost on a good team. Not defence. Not attack. Not midfield. It is about the complete puzzle. For every stat showing how a good defence won a league, there will be one that shows a bad attack got relegated (Birmingham City springs to my mind - good defence, **** attack). Look at Saints, if our attack had been good this season in front of goal, we could well have been right on the top four by early December.
CBs have to have positional intelligence and composure under pressure. They're the penultimate line of defence and any mistake from them can be costly. So yes they are important.
Obviously titles are not won solely because of good defences. But I believe it is easier to over achieve on the back of a good defence than it is on the back of a good attack. Mainly because a team can get lucky going forward and nick a few goals through penalties, corners, free kicks and win by small margins. Whereas if a poor defence get lucky, it could result in a striker missing a one-on-one, but they will likely still have other opportunities to score. Of course you are correct that it is a good team that leads to success, but it is my belief that organising the defending is slightly more important than organising the attack.
In the book Soccernomics there's proof that not conceding a goal is worth far more points than scoring one. It's a book genuinely worth a read. Vin