Objectively: in a way that is not influenced by personal feelings or opinions.
''examples I can bring up, all of which I have encountered personally''
Note I said it depends on the drug. Now (I'm quoting here) 'Generic drugs are required to have the same active ingredient, strength, dosage form, and route of administration as the brand name product. Generic drugs do not need to contain the same inactive ingredients as the brand name'.
So, as per my example above, if I want to buy a 200mg Neurofen tablet (or a strip of them) I can pay £3 for a box of brand name or I can pay £1.00 for a supermarket generic version.
There's a consumer company over here called 'Which'. For years it's tested and compared products. One such test compared a bunch of brand name Neurofen products. All made by the same company but one was for neck pain, one for back pain and so on. Every one tested out as the same. No difference what so ever. Then we have newspaper reports of generic vs brand and (again as above) IF the ingredients were identical in every way there was no difference except in price.
You yourself say 'Basically, the great majority of the raws come from China, so all companies end up with the same product. But then the differences come into place when some companies filter and clean these raws more thoroughly than others.'
Objectivity needs to be what it said it is. Even in your dads example science argues that a one off result doesn't prove a theory.
To be clear - in the argument of branded vs generic - you must compare like with like. If there are missing or added ingredients, if the active ingredients are different in amounts or form then you are NOT comparing like with like. Where the above is identical in every way you pay a higher price for the branded name and or perception of value.
Regarding perception of value over actual value. It's a very, very simple trick. I can take two identical products - made to the same quality in every way. I sell one on street corners in a plain brown box dressed casually. The other I put on a white coat, stick a pen in my pocket and maybe add a stethoscope. I also make the box a white one. And instead I sell it in a store. Guess which one people trust the most?
When I say "personally," I don't mean that it is a subjective perception - I mean that I have seen the case with my own eyes, and not just heard it from some Joe from the street. And I believe what I see, and I believe the measurements that are taken by medical equipment.
The example I have brought up with my father is not a single case - this issue has been going on for years already, and I don't see how placebo effect can decrease his blood sugar by 300% (yes, three hundred percent) more effectively. Every time he gets back to the generic, his blood sugar raises big time, and when he takes the branded metformin, blood sugar is in check.
Just recently I have observed the exact same situation with my mother, who was taking a generic against increased blood pressure, and it did not help her at all. Then she took the exact same medicine, but a branded one from Japan, took half the dosage and her blood pressure decreased. And let me tell you that there is no placebo effect either, because she is an elderly person who has no idea of the generics and brands - she just takes whatever I get for her.
Let me give you an analogy - take the indian car Tata, and the German Mercedes. The ingredients are all the same, and supposedly the manufacturing process in general lines is the same - but a Tata will never be as good as even the shittiest Mercedes.
The same thing goes with original phones, and fake Chinese iPhones. Hell - they may even be produced at the same factory, but they are not the same.
It is not only about having ingredients as such - it is about their quality, and the quality of the manufacturing process.
As I have also mentioned, I worked in a project of a pharma plant, and I have seen from inside how the difference is made between the meds. Some companies will get additional equipment to filter those raw materials from China, others will get even more equipment. In the end, when you filter the raw materials 3-4 times in comparison to 0-1 times, you end up with less active substance. Here you already get the price increase - additional equipment and machinery, and more raw material needed in order to get the right amount of purified active substance.