Just so everyone's aware of the differences between a ROTJ Biker and a Mando Biker, and also the second pic is how "doughy diaper dude" (that HT seems to have used as primary model for their Biker set-up) actually wears his costume in the eps of Mando...
-- entire cumberbund/pouch belt worn either lower or much lower in Mando
-- chest armor much longer (giving "saggy ****s" look as some have said) in Mando
-- shoulder armor longer in Mando
-- elbow and forearm armor narrower in Mando
-- pouches larger, longer and more doughy in Mando (In ROTJ they are quite boxy)
-- while similar, knee armor more boxy in Mando and slightly different design (and worn upside and higher)
The rest, helmet included, have only extremely minor differences. Also, the armor and helmets seen in ROTJ all have noticeable differences due to hand manufacture (for example, some ROTJ scouts have larger black goggles than others)
Also, the Mando speeder bike, while very similar, has numerous differences to the ROTJ version - it is not simply a ROTJ bike painted white.
Doughy diaper dude from Mando is shown next to one of the pudgier Bikers from ROTJ (there is a barely-glimpsed overweight short guy that played a ROTJ Biker Scout, and the costume does get a bit bunched and diaper looking on him) as comparison to show that the diaper look I think was intentional because the Bikers in Mando were meant to be funny: