you have no way of being confident that your certified product does not contain approved products.
That’s true. I also didn’t say hashgochas are perfect. We’re kind of playing the odds. I’m not backtracking (I used the word maaleh for certified, I didn’t passel approved), although I’m probably not explaining myself well.
Other than homemade, there’s no guarantee of kashrus even with the best hechsherim (the Satmar rov Zt”l didn’t like the term “mehadrin” for this reason). When we’re too lazy or busy to make everything from scratch, we try to get as close, in reliability, as possible. Of course it would be great to have mashgiach temidi for everything, but we don’t want to pay the price. So we employ all types of methods of keeping the food kosher al pi din, in the most economical way.
Even if one more step in the process is supervised, the level of reliability has gone up. So if there are legitimate grounds to be mattir, for example, unflavered beer without a hechsher, there is still a market for certified beer, as evidenced by the fact that there are now many beers with hechsherim (not muchrach, I know, because it’s good marketing for non-religious reasons as well).
Still, I would prefer popa’s home brew (it’s probably a thousand time tastier as well, but that’s besides the point). And I know that popa uses approved components, but we have a maaleh in one step of the process.
I’ll give you a moshol. There was once a king who needed to go to the bank to withdraw money. He walked up to the teller to withdraw money, and presented his ATM card. He was about to put in his pin #, when his trusted advisor told him (in pig latin) to cover the buttons so that the teller couldn’t see. Now, the computer techs at the bank could hack into his account, and so could some hacker in Nigeria (or wherever hackers are from). The advisor himself knows the pin as well, so the king could easily taaneh that there’s no guarantee that his money is safe, so who cares if one more person, the teller, has the pin? But it would not be a good taaneh, because prudence still dictates minimizing exposure to risk.
So too by us. Even if hechsherim rely on approved components when necessary, why wouldn’t I want something which was processed and finished (usually the most kashrus sensitive area) under supervision? Sure, if I was making a sholom zochor and couldn’t find certified beer, I would use approved. But when certified is available, I buy that. And if I had the time and know-how (and wasn’t afraid of explosions) I would make my own.