It would have made sense when you are developing newer system, the design is similar, the engines are already proven, EO are proven, as there are similar drones already exists & flying with same specs, weight category & ranges, you always don't have to reinvent the wheel,3-4 years is standard minimum regardless of weapon system being developed.
From concept phase to design phase to prototyping, internal testing, user validation testing, certification.
If we are developing lets say a new combat knife for soldier expect it to take this minimum time.
At the time the drone will come into production, a new requirement & techs would already come up, as you already given the e.g of anduril systems, when the systems are already developed & you have the data, the time frame will reduced
harop in the service, now Adani is making the longer variants, with whom CSIR drones shares similar design, how exactly is the drone gonna beat them if it's not providing a unique solution, 



