DD avoids the heat issues of hub motors
Thane delimitation, motor over heating. Because of this there is some ok ones
Hub motors are smaller underpowered, over heat, restriction of choice of thane and wheels. Hummus look as tho thay might brake this trend but still having issues bring to market. There a bit of a unicorn on the 2nd hand market
as of right now i actually believe (having ridden a couple different dds) that hummies are probably better at almost all these issues then dds.
the only dd i actually have enjoyed riding is carvons. the rest have either got major issues or are way underpowered and have trucks i dont enjoy (dkp)
possibly tb are better however their issues mean i wont buy atm
because of this i believe that hummies are currently the best choice for a drivetrain meant for freerolling and silence