Yes you are speaking about economies of scale which I clearly acknowledged in the comment you quoted. However we are not talking about ford cars or commercial airliners which mass produce. We're talking about airforce of a country which is nowhere near to mass produce Kowsar and has an immediate need to have a stop gap. Also in an airforce you dont train a pilot to fly F-14, Mig and maybe an F-4, like you can cross train cabin crew of an airliner with Airbus and Boeing. A pilot can only ever be trained for one type of aircraft, which is why I say that, other than the initial economies of scale discount on the unit price of the aircraft, over time you still have to pay more or less the same for training and maintenance if you were to train 20 pilots in 3 different types of aircraft, as opposed to 60 pilots in one.
That's why you have to compare apples with apples and look to see how many different types of fighters rival nations have in their airforce, and what you will see is not just one type. Israel has 3 (F-15, 16 and F-35), Saudi has 3 (Tornado, Eurofighter and F-15), Pakistan has 3 (F-16, J-17, J-10), and India has 6 (Su-30, Rafael, Tejas, Mig-29, Mirage 2000, and mig-21). If Iran were to add Kowsar and Su-35 they would also have 6 to add to F-14, mig 29, Mirage F-1 and F-7. So it is totally acceptable to have a few different types of aircraft in an airforce. However I'm sure they would ditch F1 and F7 if Su-35 and Kowsar come into service, surely, which would be 4 fighter types.
Yes in the long run having your own aircraft in house is the best. Nobody is disputing that, but we're talking about how realistic it is to get there at all, what sort of timescale do we have to wait to get there and what do we do in the meantime until we get there? Yeah well grippen and f-16 will never happen so bringing it up in the discussion is absolutely a waste of time.
As great as it is as a stepping stone in developing a great fighter but when I see kowsar I see target practice for western jets. So in that regard su-35 would be a more proven jet until a vastly improved kowsar or something even better comes along. What I also don't understand is why do we have to be black and white about it, why cant Iran develop Kowsar in the long run instead of rushing it and at the same time have a few stop gap Su-35 for protection? Kowsar is an unfinished product and the timescales we're talking about are decades, so what do we do in the mean time? Do we buy foreign, if that's even possible because I doubt su-35 will come, OR do we do nothing and rely on drones and missiles for x amount of decades until Kowsar is developed, which is pretty much what Iran is doing now?