@muhammad.irtiza, keeping my opinion short, the reason you gave DYL 70 is not genuine because it was not from Yamaha, Yamaha already left by that time. Secondly it was just another copy like any other Chondas. If I am wrong provide me Yamaha official link for that DYL 70 or even the engine used in it.
We talk about R&D and market survey. Yamaha might not need to go far, they can simply pick the case study of Suzuki GD-110s. It is lower in cc, it is priced insanely, it has many drawbacks (expensive spare parts, average fuel economy, ground clearance) but still a success.
YB(R) unfortunately lacks in the department of quality as I have observed. Engine is totally on the downside, with its unwanted noises, poor buddy has to pull the body load. I know its an international model and a success outside but Pakistan is a different story.