reading through some of the above comments, i'll answer a few things, i'm not a snob about the parts/brands, if they were consistently good and felt positive to use i'd not have even started this thread or ever moaned about them, if something is good i'd be using it, the fact that i am moaning suggests i don't think they are good, because generally they are not, i don't think it's snobby to say this product is generally better than that product.
@wynne 9 times out of 10 when i see oil/contamination on rotors it's not because of leaking pistons, it's mostly uneducated people spraying lube on their chains and covering the discs. but this is sort of another grumble, not that oil on rim brakes wouldn't make a difference but it doesn't affect it as much (excess chain oil dripping on the rim is the usual way it gets there) and can be easily wiped off. obvs i try to educate the novice in to not doing this regardless of the brake design.
also i think what lever they are attached to also makes a difference, for example sram brakes tend to have a spongey feel generally (in my opinion) compared to shimano, do tektro brakes feel better fitted to shimano? the bike i have in the shop with sram levers connected to spyres suggests yes as i recently set up the same brake on a sora lever and that felt much nicer but still not great to be honest.
i also accept that sometimes it's just a preference to have cable discs, but my logic suggests otherwise, i think it's related to the purchase price of the bike, and if that customers budget is that price then they will buy it reagardless of the brake design/spec. but for example, back in the day say a manufacturer had 9 bikes in a range, there would be 3 different frames, the basic 3 getting 3 different specs, then the midrange frame got 3 different specs, then the nice frame got 3 different specs, this gave you 9 price points with justifiable price jumps, on road bikes for example now you have a different way of doing it, they produce 1 frame for the basic road model, maybe 2 spec choices, both rim brake, the next frame will be a disc frame, but here's the rub, you have say a Tiagra equipped bike with rim brakes, then 2 models above you have a 105 hydraulic disc equipped bike and the price difference can be massive, as a result the manufacturer needs to fill a price point, the don't do a 105 rim brake bike to fill the mid point (which i think they should) no they do a tiagra equipped disc cable bike because that way they can build more of the disc frames and only one model of rim frame. basically reducing their costs. my point is that they only make the cable disc equipped model to fill a price point in between 2 models that do sell.
personally on a road bike i'd have rim brakes over any cable brake, so i think the manufacturers should go sora rim, tiagra rim, 105 rim, but also have tiagra disc and 105 disc, ultegra disc, dura ace disc, this would give the same price points as using cable discs with out the fear of problem brakes. gravel wise if budget is an issue and you want hydraulic brakes i'd go for something like an Orange Speedwork which is basically a flat bar gravel bike but it saves 400 over their equivalent drop bar gravel bike. i'd rather see mini v brakes on entry level gravel bikes than basic cable discs.
the other thing i'd point out is pretty much everyone on this forum has been riding for years, a wealth of experience etc, the average buyer of an £800 gravel bike is still a novice, having to deal with that person generally when they've come in to the shop with brakes that don't work very well and even when fully sorted out the brakes are not that great is far from ideal, obvs i want the customer to have good working brakes, if i could get that consistently from cable brakes it would make my life so much easier as when they ask about a hydraulic upgrade and you say "well the tiagra set up is nearly £500 and you'll need to upgrade you chain, cassette and rear mech at the minimum as well", why? because hydraulic starts at 10speed and they have 8 maybe 9 speed. it sucks, it really does.
