Have other vendors managed to make it work though, or are you just not seeing the error messages? Because I had sync problems with Apple Notes - one of Apple’s own products! - for over 9 months last year and I never once got an error message. I only knew because I could physically see that files were missing from devices. DT is reporting the errors, but most apps don’t.
In any case you’re repeatedly mixing up different iCloud sync mechanisms in this thread, which makes me believe you don’t really understand the complexity of the problem, which in turn explains why you don’t understand that it’s an Apple problem not a DT problem.
Your subject header and the error code you’ve reported are not the same either, leaving me (and probably others) unsure as to which error code you are getting “every time”. If it’s error 15, waiting 30 seconds and trying again usually fixes the issue for me. I find this error to be sporadic and a second attempt usually works when it appears. It makes little difference to the usage of DT for me, and I understand that the issue of the sync is out of their hands and I have voluntarily chosen to use a sync that many have been reporting as underperforming for several years now.