Well, my novel's fights....
In the early novel, they were mostly RPG based, with a lot of numbers and rolls, but in the later section of the novel my main characters "outgrew" that type of fighting, because they became so ridiculously overpowered that it didn't even matter.
My fights were certainly much longer at first, as they were even fights, but they still were very short.
Now, if I look at fights among other characters in my novel (Non mc characters), these fights are also pretty damn short. The longest fights are only maybe 2 or 3 pages at max.
I suppose this is partially because my fights are pure fights.
There is not a lot of dialogue. This goes on either before or after the fight for me. Many animes and mangas tend to fill a fight with dialogue, but I kind of despise that sort of thing. When youre at the fight, just fight. That's all.
2nd, because it takes only a few sentences to describe a series of motions, which would take much longer to play out in an anime or in real life.
If I really want a fight to be long, I have to add in a ton of mechanics and new things to the fight, and be constantly introducing these elements. My brain can only think up so much stuff, so eventually it will come to an end. Though, this is only referring to individual fights.
What about the more long term grand scheme battles?
These are much different, but not that much so since my mcs are completely overpowered.
I had one arc that was a war arc. And this war lasted an entire Volume. There were many developments, and plenty of fighting throughout the volume, however one thing to note is that even the fights here were only prolongued because there were many people fighting at once.
But as far as individual fighting which doesn't have twists and turns like a war does, I often find that it only lasts a few lines before someone dies. I am trying to introduce a real big long fight to the end of the Volume I am currently writing by having an enemy which starts out weaker than the character they are fighting, who is being extremely careful and thus does not immediately finish them off, but then powers up significantly to make it a much better fight. I have a lot of ideas going into this fight to make it longer than most, but even then it won't last more than a chapter. (My chapters are around 3k words)