How are you defining "free content"?
If it's content that is available on Free-to-view other services (Freeview or Freesat), then I would dispute your figure of 90%. I have well over 200 TV channels available on Sky, and only about 30 available on Freeview and approx 160 on Freesat. All have at least some +1 channels, so not all of those channels contain unique content.
If you are saying that it is available through the Sky infrastructure without having a Sky subscription, then I may be in slightly closer agreement with you, but try try removing your Sky subscription card and seeing how may channels you can no longer get.
For my ~£60 a month for a Sky HD package, in addition to the Freeview channels, I get Sky 1, Sky Atlantic, Sky Living, all of which contain content not available anywhere else in the UK, and I also get SyFy, Sky Arts, a host of documentary channels, access to 'golden' channels like Watch, a moderate selection of movie channels (although not as good as they were) and also a whole host of on-demand content which I would not pay any extra for. On top of that, they gave me the box(es) for free (they replaced my original SkyHD box without cost when they rolled out the on-demand services).
I don't agree with the way that they spread the desirable content across as many packages as they can to maximise the number of packages you need to buy, and I certainly don't agree with the gouging of their customers with regard to sports channels, but I don't think it is such bad value.
If they still existed (and this is mostly the reason why they don't), I certainly would no longer rent any DVDs from places like Blockbuster, and I've noticed that the number of DVDs I buy has dropped significantly since Sky installed their on-demand service. So in recent years, the amount of money I've spent on content has actually declined as Sky have brought on their services. This seems good to me!
I am reluctant to become a triple-pay customer, because I don't actually like Sky's business model much, but I don't really object to getting TV from them.