Yeah you are right - but a lot of people who use this stuff are unfortunately ignorant. Just want to fill a shirt and don't really want to bother researching, planning or investing money into a good cycle.
As for the stacks - for me it is all about control, I'd rather buy separate for my stack and then like you said you can trial run individually, add or remove, increase or decrease separately and you have more control that way. If that all in one stack works for you - you essentially have to buy the same again next time cos it could be any one of the 3 or more compounds doing the work like you said - like wise if you have a bad reaction you have to write off all 3 compounds in the future unless you want to trial run them all individually like Russian roulette to find the culprit. I have nothing against stacked products if they are responsible and realistically dosed. Like 5mg superdrol & 30mg MX LMG for example - not like 10mg SD 30mg DMZ and 10mg Trenavar - just stupid dosages that aren't really a proportionate or safe stack