I don't think BD needs to wait that long. Chinese are able to supply J-10 very fast. 80 aircraft can be ordered right now and the order can be fulfilled in 3-4 years. We don't have the luxury of time, it has become very urgent now. As for diversification of hardware, I agree. If it was up to me, I would have ordered an aircraft manufacturing plant as well, with some aircraft coming from China, the rest being assembled or manufactured in BD.
Our small minded low class politicians neither have the vision nor the will to do anything like that. But if BD really wanted, it's completely within our financial capability to build a military the size of that of Pakistan's.
Vast majority of AFs in the region will have bulk of their inventory with 4.5 gen. An AF can't have all high tech, you need a work horse that does most of the job cheaply while high end being the tip of the spear.