Interesting. I have only personally experienced hydraulics, so I can't compare with mechanicals.
I can say that Avid/Sram are a PAIN!!! to bleed, you gotta use these special syringes to create vacuums at both ends to get microscopic bubbles out of DOT fluid, follow a very specific workflow and only do it on a 5th tuesday when there's a full moon. Also my Avids had very bad turkey gobble, until a friend advised me to dab a little grease on the back of the brake pads, that took care of it.
I've found Shimano hydraulics dead easy though, they work great, they use nontoxic mineral oil, and you don't even really need to bleed them, you can just open the top port and 'burp' them by flexing the lever until no more air comes out (which I guess is the same as 'until they're firm', although you don't really know until you close up the port again)
With no experience, I can't compare hydraulic vs mech modulation. You're right, on/off is the opposite of modulation. All I know is, my hydraulics have much better modulation than the V brakes on my old GT mtb. (When my wife started mtb'ing with those brakes, she had a lot of endos and had to learn to be very careful with the front brake) And they are strong enough I can get away with 1 finger braking most of the time, 2 fingers if I happen to be descending a big hill and have to ride the brakes the whole way.
I've also found it difficult to get hydraulics well aligned/centered. The notion of loosen the mounting bolts, squeeze the brake, and tighten them back up, doesn't work that well in practice. But I imagine it would be the same with mechanicals.