Your first sentence, I agree with.It's all relative....
The whole DE saving thing is an urban legend.
I've used DE for the last 4 years, carts and disposables for the 12 before that.
Back home, water quality is really terrible. The salt will eat away at blades really quickly, no matter how well you clean them. This reduced the life of my fusion cartridges to barely 2 or 3 shaves. It became forbiddingly expensive quite soon. Any DE blade gave me at least 2 shaves with a simple flip and its tons cheaper.
And living in England, I've pretty much seen the same issue with carts. Water quality is just fine, but living close to the sea and with terrible weather, everything's damp and blades still corrode fast. Cheap disposables may work, but you're not going to get a BBS from them. I still save quite a lot with DE and indulge on new razors and aftershaves.
So yeah, DE does save a lot for the right person.