I am actually getting same accuracy in both CA (not more than 4x4)/Duel (25-35%, depending on ping, opponents dodging and Acapulco weather I guess). But I have noticed that when I'm busy thinking about opponents location, item timing and such things involved in Duel, I somehow get distracted while aiming.
And I have started playing CA for aiming purposes only, so I can say it really helps. I used to get outshafted every situation with even stacks, now I sometimes can actually pull some fights off even with lesser stack, not mentioning that if I manage to catch enemy off guard, I literally burn him to hell with none incoming damage at all.
Muscle memory is all the same in every gametype.
The only problem I see here, is that playing TS and EtE you are getting used to fight on plain grounds, no ladders or boxes whatsoever, so when you use shaft in Duels, there are many occasions you have to use different arm motions in comparison to practice matches. Instead of short dodging and short aim adjustments you need to perform long and slow arm swipe while jumping somewhere to a higher ground and this could be tricky. Dm13 shards/PG area, jumppad/LG ammo area are all about that.
Nevertheless, QL is a shooter, so practicing your aim will definitely make you better in any gametype.