Yes, but not the way they produced the G4.... A boot loop issue that continues seamlessly to several serial numbers... There is an obviously serious quality issue with LG. I love my LG G3, no issues but my next one is not going to be a LG for sure. Even thought I am happy with my G3, I do not trust LG.
While I understand your sentiment, I personally feel both more and less skeptical about phone manufacturers. From a consumer's perspective, I agree it would have been preferable if LG had realized early on that there was a design or manufacturing flaw in the board layout of the G4 that would eventually cause those many of those boards to fail.
But I also have essentially no knowledge of manufacturing processes. We don't know if it was a flaw in the actual design of the board or whether it crept in during the manufacturing process, and thus whether one could ultimately blame LG or, say, Foxconn for this issue (or whoever is actually manufacturing the phone; if it was manufactured by an LG-owned factory in Korea, it would still be separate from the research & design facility). LIke any smartphone manufacturer, LG doesn't want to give consumers that kind of knowledge, and they are not going to tell you where the problem occurred, only that they 'fixed' it.
I have honestly no idea how hard (or easy) it would be for a manufacturer to spot this particular issue through QA processes alone, although I do believe that phones are usually being stress-tested early on during the manufacturing cycle to find issues just like this one. They are being cooked in ovens, for example, to simulate a large number of heat cycles.
I think it is safe to assume that the initial production run is usually the largest, especially with flagship smartphones that don't sell like hotcakes for much longer than a few months each, so that *if* a major problem like this occurs, it's not going to be easy to manufacture a large number of 'fixed' boards later. (That's why they spend money on stress tests.)
But here's another data point: years ago, by way of example, Nvidia had a similar problem with a wrong or defective substrate on some of their laptop GPUs, which eventually led to a very large number of these GPUs to fail after a certain amount of use (heat-up cycles). An electrical connection broke, and the whole board had to be replaced because the GPU was soldered onto it. I was affected by this, the laptop OEM replaced the motherboard under warranty, but the GPU on the new board had the same issue and died the same way after about the same time. Of course people were upset about it, but many probably also realized that this kind of problem can hit the market leader as well as the smaller players in a highly commoditized market.
At this point, I would posit that a smartphone is a smartphone is a smartphone. The same factories that make iPhones also make Samsung S7 Edges and perhaps the G4/G5s of this world too. Apple, Samsung and Motorola would hate for you to realize this though, because they need and want your brand loyalty. They defeintely do not want you to think of a smartphone as a commodity item.
QA is a problem that isn't easy to solve, and unless you, the consumer, have a deep level of insight into the manufacturing process of each phone you take into consideration (and most likely you do not, because companies are extremely tight-lipped about that), then your best bet is probably to leave brand loyalties behind and strictly buy your next phone based on your own needs regarding features, design, UI/bloatware, security updates, availability of accessories, length of warranty, the reputation of their customer service etc.