So, first point: okay I'll admit, a really thrilling, great book is as absorbing as any given thing online; more so, maybe. The thing is though, that if a book (one which is perhaps less than the absolute thrillingest 100% great book -- an 80% book, if you will) lags, and you come up out of it, there you are in physical space. The next book is not a mere click away.
As for the second thing; I think we're talking about different phenomena, or at least different time scales. When you say "I remember being bored a few times during summers before high school", you are apparently (I think) talking about extended periods -- "that day I was bored" or at least "those two hours I was bored". You are not remembering instances of five minutes when you were bored. And if you have "almost never been really bored" as an adult, we are definitely not talking about the same thing.
Boredom is a kind of pain. As such, it is a signal. If you sit in an uncomfortable position for a long time, your body will begin to send you pain, as a signal that you should move. This signal is precious. Your body is telling you what it needs. The same is true of various other kinds of pain. When someone is treating you badly, and your feelings are hurt, it's a signal of something awry in the relationship.
That doesn't mean we want to stay in pain. We don't want to be trapped sitting in an uncomfortable position, we don't want to leave our hands on the stove, we don't want to ignore the signs that a relationship is out of balance. Being trapped in pain is not a good thing.
On the other hand, though, we also don't want to mask signals of pain so that we simply don't perceive them. If we block out the signal that the body is sending, that we should move, we eventually start doing ourselves damage. If we totally block out the feeling of discomfort in a relationship, we are likely to get more deeply hurt.
It's also not always useful to us if someone else responds to the signal, or avoids us ever receiving it. It keeps us from being independent and self-directing. Perhaps someone could avoid your ever feeling physical discomfort if they always arranged your limbs for you, perhaps they could escort you through parties and always steer you clear of dull conversationalists, and so on. But that would make you more passive, and interfere with your autonomy.
If you remember distinctly, years later, times during summers when you were bored and nothing good came of it, it sounds like you got trapped being bored -- just as, as an adult, you might get trapped by a boorish pontificator at a party. It's even possible that, if you were stuck there long enough, it would have been optimal -- at some point for an adult to come help you figure out how to get past whatever was keeping you stuck.
(...which would be interesting to know. What were some of the times you were bored. Why were you bored? Why were you then not bored all those other, similar times -- the other summers where you read or swam or hung out with people instead of being bored? What was different the times you were bored for extended periods of time? Was it, perhaps, that there was a specific need that had become urgent and you hadn't figured out how to meet it? That's sort of what I imagine: "there's no one (that I like) to play with and I don't feel like reading or biking or..."... translation: I am receiving the signal, all right, but I don't know how to obtain the thing it's telling me I need. That's a different problem than just "boredom sucks".)
Anyway, what you're talking about here is not the same phenomenon I'm talking about. I have never seen my kids stay bored for an entire hour straight, and probably not even twenty minutes. What I'm talking about is that moment at which, removed forcibly (albeit by their own prior consent) from that supernormal stimulus, the fascinating, all-encompassing stimulation cornucopia of The Computer, they howl: "I'm bored!! There's Nothing To Do!"
This happens less frequently than it used to, but it still happens.
They're not lying. They are bored. They are intensely bored -- we're talking, here, about an intense boredom of five or ten minutes duration. They are looking for someone or something else to do the work of getting them engaged in the next project, the next thing.
Now, I play with my kids a LOT. I play with them all the time. My kids are among my favorite people to play with, and I have a long mental list of things I want to do with them, when they have a minute.
Nonetheless, in that moment when they are experiencing boredom -- short-term, what's-next boredom -- I have learned to be cautious about jumping in and providing them with the next round of stimulation. I could handle that signal of boredom-pain for them. Given that their lives are already pretty scheduled -- school, music lessons, sports classes, parties, etc. -- and that they are often out with friends, I could easily fill the remaining "free hours" with my ideas for what they should be doing, such that they would never be bored even for five minutes.
But I hold back. Because if they find their own way through the impasse, they have ownership of what they decide to do next. Thing is, there are plenty of options -- it's a house full of books and toys and games, they have chores to do, they like to cook, there are friends nearby, and I could be talked into doing some specific activity. So if, in the first moment, none of those options appeals -- if they loll around saying "I'm booorrred" in a house full of things to do, I figure there's something else going on there. There's some need they have they haven't figured out yet. They could perhaps be talked into a game of poker or basketball or whatever, distracted from the new and inchoate need, and it might be enough to dispel, or at least stifle, that signal of boredom-pain. But if nothing like that is thrust on them, if they are allowed to develop their own ideas, to unearth that need and find a way to fill it, they move forward.
That's what I mean about creating and owning your time. Your own decisions, your own sovereignty over what you do, even when it becomes difficult, even when you feel stuck.
Now if they were stuck for really extended periods of time, and it was really getting them down, I would try to figure out what was blocking them, where they needed a hand. But I would be cautious of rushing in and doing it for them. I think often, the longer they are "bored" -- if it's ten minutes rather than thirty seconds, say; or even a day or a week of engaging in activities, but expressing dissatisfaction with them -- the more awesome the thing they are going to come up with on the other side of it is. "Boredom" is often what the difficult, uncertain stage of creativity looks like.
I am interested in your general peeve about "imperfection is good". I think imperfection generally is good. Ignoring or avoiding obvious optimizations out of pique, spite or perversity is not good. But that isn't the same thing. The cost of perfection is very often low ambitions. If you have managed to perfect everything, it's because you've tightly constrained the scope; at that point, you need to break it open, expand the feature set, raise the bar, the immediate result of which is imperfection. You cannot expand the feature set without writing some bugs. So as a general rule, the presence of imperfection is a necessary, though not a sufficient, indication of growth and of the good life.