You just described how it's not either/or but some of each. You want some thinness and lightness, and some power. You want the balance you want, others want a different balance. Again, it's a subjective preference. It's not stupid to have a different preference than you do.
One reason 13" machines are so popular is that people really do want something smaller and lighter, and are willing to trade performance and features for that. The same applies to the 15". The 17" wasn't popular enough to survive.
It's a mistake to think Apple didn't use desktop RAM only because of thinness and lightness, mythology notwithstanding. It would make the machine bigger and heavier, but it would also reduce battery life even with a maximum-sized battery. I know, you don't care, but many do.
Again, all laptops involve compromise of size and weight with performance and features. All, without exception.
And for the record, the 2016 is improved over the 2015 in easily a dozen significant ways.