To make your own summaries you need to understand and think about the source material. I get more value from reading the book and analyzing it rather than glancing at the too-long-didn't-read version of notes somebody else wrote.
For example, the entire Checklist Manifesto book can be distilled to one sentence: break down crucial procedures into checklists and follow them. That's the core message. The 1%. On its own it means nothing to me. I can re-read it hundreds of times and it won't change my life. I'll recognize it but I won't understand it.
I need time to process my thoughts. Let the ideas marinate in my brain so to speak. I won't get much out of a book if I read it cover to cover in one sitting either.
My way to study a subject is to read not just one book, but 2 or 3 more from different authors. This way I can compare their opinions, find common things, see where they disagree, find the answers to questions I wrote down during my first read. Then I can take those ideas and make them my own.
Yes, it takes time. There's no shortcuts when I want to understand something.
As for the 99% filler content - I don't have to read it. When I read I ask myself "What's the goal of this section? What does the author try to achieve?". Often, I find a good reason. If not, I'll skip it. I can always return to it later. I have that option. I can't do that with summaries because they are lossy compression. I can't get more out of them because it's not there.
Sure, I can do my own research and look for it on the internet or interview relevant people. But at this point, I might as well write my own book.