As far as I know we are the only platform that you can program a specific resistance (slope) and use them in intervals for time for example. Now Rouvy allows you to upload a route that has a slope to it so theoretically anyone that allows importing a route kind of supports this but that is much more convoluted process than using our slopes instead of resistance 
So we have a few users here that have built spreadsheets that convert slope x cadence to watts. If ultimately you are trying to target watts for a specific cadence then I think it’s ultimately the same either way meaning. You need to have a formula unless you always use the same RPM, then you could memorize it. If you are going to have a forumla to determine your slope targets then I would think it is basically the same whether it is resistance or slope.
So resistance % is specific to your trainer, so saying I am holding a specific resistance percent is the same as saying I am holding a specific slope degrees although slope degrees translates better from device to deivce. I would think if you prefer to say resistance it’s probably simple math like slope times 3 or something.
I would be happy to be the best app for velodrome cyclists
We try to support what we consider underserved needs as long as they are not too small of niche 
If I am wrong about my thinking regarding needing to use excel anyway and with resistance you could do it with excel because you are not focused on watts as much as newton meters (resistance) and rpm and this really made the difference by supporting automatated resistance mode as I said I would consider it because it should not be too hard.