If you are serious about history then you have to read books written by historians. There is no shortcut. "What if those books make history more complicated?" They will; that is the point of a deeper understanding of history, to understand it is complicated. "History books are almost always 600 pages long." This is less commonly the case anymore, for what it is worth (my book was 500 pages long but that was considered exceptionally long; today most publishers pressure you to have it be more like 200-300 pages long). "They also overuse adjectives." This is a weird thing to get hung up on (whether true or not; I doubt it is uniquely true of history books) and sounds a bit like an excuse not to read books.

But anyway — if you want to study history seriously, you have to read books. There is no shortcut. The more you read, the easier they will get to read and make sense of — historical understanding is additive, in that everything you read is going to build upon what you've already read. So it's hard when you're starting out.

Wikipedia is a bad source for real understanding of history, and downloading random PDFs is not going to fix any of your issues.

I mean, the closest thing to a 'shortcut' to understanding specific events in history is, well, AskHistorians. But the point of this place is that those of us who write in AskHistorians, even if many of our answerers and flairs aren't historians by training or profession, have nevertheless read those history books, the long, the short, the boring, the exciting. And the main problem with what you're describing is this: it seems like you want to find a panacea, and panaceas aren't real. You dislike oversimplification, but you also dislike long and detailed explanations. There's no such thing as an 'appropriate' amount of description regarding anything in history.

History is an exceptionally complicated field for a plethora of reasons. Chief among them is the fact that, as Enrique Moradiellos explains, history as a discipline lacks what most sciences tend to have: a clearly defined, palpable object/subject to study, because the past no longer exists. Time is quite literally immaterial, and what's already occurred cannot be observed directly; we can only observe the past through what's left. Evidences, relics, sources, collective memory. The work historians do in order to create those books you describe as too long and unnecessarily descriptive is immense, it requires us to spend hundreds of hours perusing archives, museums, libraries, conducting interviews, transcribing and trimming said interviews in order to make them useful, reviewing primary and secondary literature, and writing. So much writing. And, perhaps more importantly, interpreting everything we've read and heard and seen. Because history is, at its core, an interpretive discipline that requires us to truly entangle ourselves in what we're studying. When you read a history book, you're not just reading what the historian heard, saw and read, but also what the person thinks about all of that. It's a deeply human discipline, and the work of a historian makes it even more human.

For instance, many of us study subjects that can be very powerful, but also very emotionally demanding and even taxing. Take me, for instance. Most of what I study revolves around music, which might not sound like the most emotionally demanding thing ever, especially when compared to say, Holocaust studies. But when you actually go into what I do, you'll find that a lot of the music I work with comes from Andean indigenous communities, and it's born from the deep and long-lasting wounds colonialism left, and the harm neocolonial extractivism is causing right now in many communities all along the mountain range. As an indigenous descendant myself, working with these histories can be extremely difficult. However, I feel a responsibility towards the memory and the realities, to the humans behind these music styles, that serves as the fuel that drives me forward. And I know for a fact that I'm hardly the only person studying history that puts a lot of their emotional energy into what they do, only to have people criticize us for being "obnoxious".

With all that in mind, if you truly care about studying history, the best advice I can provide is to be respectful of the human behind the book. Don't disrespect people just because they don't write exactly in the way you demand. You won't even find something that conforms to your every desire in literature. Respecting the human being behind the book might allow you to look at them in a different light.

As restricteddata wrote. Read historians. Sure anyone can write history, let say economists, philosophers, biologists, etc.. And they can be as good in terms of historiograpchical standards compared to a historians work. But we are the ones that are in constant reflexion about it, so i would recommend you check out books about historiography like The French Historical Revolution: The Anneles School - Peter Burke or those alike if your are interested in a specific "regional school" or by area of studies like english marxist social history or watteva your into. Sure the books or papers about historiography arent the fun ones, yet, as history dosent exist knowing about the develovment of the writing of history is fundamental to understand it.

Also about "good sources" you could try to check out the academic journals, Past and Present for example is (or was?) one of the most important english journals... is paid tho'... but theres plenty of other "free" journals whit high standards.