Idk about anyone else, but I was CRAZY about historical fusion dramas. I would auto-watch it unless it's a romance-focused one without other interesting plot elements. Even then, I am extremely fond of historical fusion more than modernistic dramas. But this is only for historical fusion dramas, which are often reimagined versions of history.
As for the real historical dramas which are more historically accurate, I'm not too attracted to those (they're long too), and they're riddled with too many complicated schemes that even writers find difficult to imagine the logic for. But historical fusion dramas tend to be shorter and have more compelling storylines. Iljimae was one of my favorites.
There are long form historical fusion dramas though. I think the only long KDrama that I sincerely followed from start to finish was The Flowers in Prison. It was long (50+ episodes, iirc), but I found it incredibly worthwhile.
Pacing tends to be the #1 issue in KDramas (which is why Youngguk once said that writers are extremely important for drama series). In long-running historical KDramas, pacing becomes even more of a problem, but The Flowers in Prison seemed to have been able to handle it gracefully. I wouldn't say it's perfect, but they did a great job. It's definitely one of my top favorites. I don't think it would have been better executed and produced. The writer(s) did a great job hanging on.
Anyways, I'm rambling, sorry. 😅