As far as I understand each camera applies it's own tone curve to the image, or am I wrong?
Initially I wanted to be brand-agnostic and instead of discussing specific sensors, I want to identify what really matters for my needs (and maybe many others). I'm not able to tell what it is right now, so everyone's input is appreciated
Not really: each camera applies its own tone curve, but that happens *after* the ADC has done its job, and, as far as I know, all cameras have linear ADC (ok, some have piecewise linear, but that's actually a change for exposure, not for the ADC, which is still linear; and I'm not sure any of the ones we're talking about actually does that).
The fact that light is linear but you see it as log makes this very inefficient, and it is the reason that, for example, some Nikon cameras (low to mid-end) apply a log curve even in their RAW files: with linear, you have way more gradation than you need in the highlights, and may still be struggling in the shadows. But even this curve happens after the ADC, so it's not what we are talking about, I think.
As for the need for DR, as I said, it depends on what you do, how much time you have to do it, and how much margin of error. My friend was carrying an extra 5-year-old 12 Mpix camera just in case, because he thought he needed to do so. If you don't think you need it, well, good for you, what can I say?
Now go ask any cinematographer if they think 11 or 12 stops of DR is enough.
(hint: I hardly ever shoot stills, I'm a vidiot)