it really is worth persevering as Cuemix is actually very flexible, other than the one restriction I stated earlier… and fwiw, its light years ahead in capability compared to the 18i20 (which I also have).
Once you have your mixes setup (essentially one mix per set of outputs) there is little to be done in the software, and from the front panel of the motu you get access to everything, in particular I find ch mutes to be real handy when used standalone, but you can access everything… also for standalone use, the fx are very well done.
in the focusrite, you cannot control anything without mixcontrol (which makes cuemix look simple and elegant) . The only control you have from the box is the ch trim/gain knobs which are very sensitive and so you are unable to accurately reset to the right level if you use these as volume knobs. (given there is no mutes)…
just my 2c
I had bought the 18i20 to use as an ADAT mux into my 828, but I think I will sell it on and save up for another 828… they are just in a different class.