Yes any device on Synology is just lost time, Synology has removed the Multimedia Stack and drivers from the system.
Sundtek drivers are rolled out with a separate TV stack which does not depend on the kernel version.
And yes there are DVB-T2 devices aailable from Sundtek.
Also pay attention when Synology updates the system Sundtek will still work - this is a big advantage, it has been like that for over 10 years.