I have noticed that most people fall into one of two categories. Never sent a gun back (or at most once), or have to send back almost every gun they buy several times to get them right. I do think there are some true lemons that get out, and those may need several trips to figure out all that is wrong. I also think we sometimes expect a Cadillac ride from a Chevette.In another post a person says you might be overthinking the situation, I tend to agree. The differences between the LC9s (which I believe you had at one time) and the EC9 are small. New models of both are still available.
I've had an LC9s for 5-6 years now. Fired just under 2400 rounds without any problems other than my thumb hit the slide lock lever and kept the sslide locked back before the mag was empty a couple of times. No trips back to the factory.
As to people who have had to send their firearms back to the factory multiple times, for a person like you, who is professionally trained in the sciences, there are some fair asumptions that can be made. Especially when that person has multiple other brands of firearms that had to go back to the factory several times each.
1. The person is extremely unlucky and buys only crappy rejects. They should never play the lottery.
2. They have some kind of issue with firearm handling or maintenance, or
3. There really is something wrong. (the fact that they have had similar problems with multiple other manufacturer's firearms makes me lean towards items 1 or 2, though.
Good luck in your quest.