If you want a strong team that optimistically works well together then set supremely high standards with risk of failure. When risk of failure to deliver becomes probable spread the tragedy across all team members. This is when your senior developers will step up to guide the juniors. Failure to do so results in whiners who throw each other under the bus.
I'm not trying to criticize you. You don't sound like a bad person or anything. But you do sound a bit resentful and dismissive of more junior engineers and their desire to use Java frameworks.
Look, software has a very real people problem. Mike Judge (Beavis and Butthead) thought as much when he wrote Office Space. If you to see how widely this is viewed by other senior developers read the comments in this other recent thread.
Yes, the subject of declining quality of tech workers is an interesting one. I first noticed it around 2014, but I think the root of it may go back into the late 2000s. It seems like a lot of people in that era started hearing that they should major in CS because it's a high paying field, and they took that advice regardless of whether they really had any inherent interest in computing or the magic of computers. This resulted in more and more people coming into the industry who seemed like they didn't quite fit, although as a manager you want to welcome everyone on your team and get them to be their most productive, so obviously you don't want to discourage anyone. I think it may be related to what you're talking about.
On the other hand, I would say that with each new generation that comes up, they are confronting a new world with increasingly high level tools, and I don't think we should disparage these folks. It isn't like I grew up on Charles Babbage's Difference Engine; I just took the field as it was at the time I happened to be a teenager.
Like in your situation, you probably started with Java when frameworks like Spring did not exist yet or were not widely used. But as those things evolved and got better, it's what the newer people would have been taught or done in previous jobs, so I don't really buy that that in and of itself makes them lesser engineers. They may just be doing the most reasonable thing with the tools that were popular at the time that they learned. Is it possible you are conflating some specific not-so-great engineers with whom you worked, with the broader trend in that period (and today) toward increasingly high level constructs as the underlying silicon gets faster and more powerful? Not sure, just offering it to you as an idea.
I'm really sorry that you wasted 15 years! I've wasted a lot of my time on the earth as well, and I think most people feel that way about some period in their life. But it sounds like you came into some ideas and insights that you wouldn't have otherwise had, even if the experience itself was frustrating. Maybe that's just the reality of life?