my logic with cable disc brakes and why they don't work well on drop bar levers, am i right?

If you want to get a bit more technical, I reckon that:
On the old MTB cable disk jobbies you have to put the pads very close to the rotor, hence, even the slightest misalignment causes disk rub. Also, on flat bars you use the full length of the lever when you press it. What it translates into, is a huge amount of leverage when you brake.
Road brakes pull half the length of the cable compared to V-brake levers, which gives you ~ 50% of your MTB force. Furthermore, you don't use the full length of the brake lever when braking from the hoods, so now you're down to, say, 25% of MTB force. And some cable pull does indeed get lost in the compressing cable housing, so you might as well be down to 15-20% of the MTB force.
If you limit your MTB lever to 1/4 of its movement, you'll never get the MTB disk caliper to work well, because even on a good day with 100% lever movement you have to set the pads really close.
Add losses in braking efficiency from slightly mis-aligned calipers, pads, rotors and you don't even get a speed modulator, never mind a brake. At least the buggers squeal so bad that everyone can hear you approaching.
A road disk caliper should therefore, have a completely different mechanical advantage to an MTB caliper. It just looks like the manufacturers never bothered with proper design & testing because there's no money in it. They must have changed it slightly by whatever ratio they picked, and never refined to the point of them actually working.

I am curious, however, that your travel adapter trick didn't work.
 
Back in the dim and distant, I used Travel Agents on a new build cable disc tourer for a customer. They were a faf to get right but the did work by multiplying the cable pull for the disc brake.

Back in the further dim and dimmer distant, I had some cable operated hydraulic calipers (which seem to have made a comeback!) that worked with cantilever lever levers

*I've just bought these https://www.ebay.co.uk/itm/16671062...lp:4429486&itmmeta=01HXYB2BGBZTYX8BCDHNCPQ0WE

because I'm a sucker for cheap tat (and some Tektro v brake road levers)
 
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We "fix" well used cable disc brakes several times a day, every day.- and you can see that the conclusions being reached in this thread are similar to what id say:

Mtb cable discs are usually as good as rim brakes and better in the wet.
This is because greater cable pull and leverage overcomes the wonky pistons, caliper mounts, cable compression and so on.

On a drop bar system, there is less standardisation, less cable pull, poorer lever movement etc. So it's harder to get it good.
But spyres can be got good - it just takes a long time and wearing in, or a lot of luck.
They also slowly become crap with use. A well used pair of spyres needs recycling.
Road Bb7s can be good, maybe easier to get working ok than spyres, and last a bit longer.
The shimano Road caliper bbr-517 can also be good.

Everything else is a bit of a gamble, or just a waste of time if it's not right. Alignment is crucial, and in cheap calipers, that's down to chance.
Cheap stuff has poorer tolerance.
I too have poorer tolerance with cheap cable discs.
 
If my frankenbike idea comes to fruition, I will be able to give a good report on shite cable brakes

The Zoom hydraulics I fitted during covid have done very well - they were about £29 in 2020 - so I'm positive for the new set
 
The Zoom hydraulics I fitted during covid have done very well - they were about £29
Begs the question as to why anyone bothers with flatbar cable discs.
Obviously with road the shifter gubbins cost more but I'm sure they'll get there eventually and cable discs will be the preserve of the Paul brigade hipsters and Argos.
 
Changed the pads on my BB7s this weekend after 4138 miles of riding. Took less than 5 minutes.

Whilst changing the pads and dialling in the adjusters I was thinking to myself how great the brakes are and how well they have performed.

Should change the cables before 5k miles but only because I want to, it’s not necessary.

They don’t have the ‘hitting a brick wall’ stopping power of my Hope hydraulics but they’re a step up from rim brakes and in thousands of miles have been totally maintenance free apart from winding in the pads to account for wear.

Brilliant.
 
Just out of interest, what levers are you using?
I've done several thousand miles on BB7road and Spyre road and at the best of times they were barely acceptable and significantly worse than rim brakes.
 
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