You're not getting what I'm saying. Anyway, the only thing voltage drop affects is the efficiency of your build or in practical terms battery life. That's it.
What I'm talking about is that every single time you press that button, you're depleting your battery a little, every subsequent time you press that button, as your battery drains, your battery is delivering slightly less voltage. From a fresh battery to a near depleted battery you're looking at a noticeably different vape.
The best you can possibly hope for is to get close for a little while from the high side, hit the target, then stay reasonably close for a while on the low side as the battery drains. Good electronics 100% overcome that downside of batteries and if I'm flavor chasing, control is (IMHO) essential to get the most out of a juice, something unregulated devices are simply not capable of.
They're just the wrong tool for the job. I've got nothing against running unregulated devices, but you just have to understand their limitations and how they operate and decide if it suits the purpose. For the most part, they work fine with most of the juices I have, 10% drift from high to low isn't that big a deal. But when I'm after getting the best flavor I can get out of a juice, or I'm using a juice that has a narrow band where it just pops, they just aren't even a consideration.
Ah, yes, you are absolutely correct on the depleted battery.
I used to use a regulated device to find the watts to optimize a juice flavor. Once I found it, I built a coil to give me that target on an unregulated device. Not quite what you are talking about, but it did work. I do vape certain juice in a regulated device in order to keep it consistent without having to change batteries to keep the volts above 4.0.