Oh bull pa-tootey. What difference does it make if it's in narration or between a pair of quotation marks?
Well, I don't rightly know, but I think you'll find most people's recommendation here hasn't been to turn this monologue into narration, it's to summarize quickly and only touch on the most important aspects and move on, or at the very least to introduce some conflict into the speech itself.
Some of the most interesting, exciting, most involved scenes in a plethora of novels has been long passages of dialogue.
I'd be willing to accept that, but your earlier example of pages describing a sword stroke felt a little bit like unfounded anecdotal and hyperbolic evidence you made up to support your opinion, and this feels a little bit like that too. I'm not so well-read so forgive me, but I can't think of a monologue in a novel that I enjoyed more than the rest of the book.
It can be said in a very few sentences? Really? Go to a movie some time and identify how many long speeches are provided there. Even in summer block-buster action movies.
Movies and books are completely different things.
What gets delivered is, has been and always will be the most important thing. Action is action. But understanding comes with speech.
I'm not really sure what you're trying to say here, but I think you're missing the point.
The OP sounds like he's got a scene where one of the main characters arrives, plants his feet, sums up everything that he's done so far, goes through his backstory a little bit, and then goes on to talk about what he intends to do next. This, to me, doesn't sound like a speech. It sounds like a business meeting. A history lesson followed by a sales pitch. That wouldn't be so bad, but the OP has also said that no one's really there to disagree with him or question anything he's saying, so it doesn't sound like there's conflict at all. That's why I'm worried about this scene, personally, and I think that's why a lot of people are worried too.
OP, my recommendation is to, first, post this speech on SYW so we can get a better idea of how it works and if it works.
Otherwise, I agree with the people who have said to find a way to cut from it, and find a way to introduce conflict. This sounds like a character that the reader will have been with most of the book, so do you have to go through the faction and justify all of the things he's done? I mean, it sounds like the reader will be familiar with the faction and the things he's done already, so trodding on that ground will just get boring, I'd think. And no one is disagreeing with him? Not even questioning him? Then why does he even have to justify himself? You say there's been assassinations, and no one is like "hey, what gives you the right to murder people?" The way you have described this speech so far has made it sound like a pretty big moment in the book, but if there's no challenge for the character--if he just gets what he wants and everyone goes with what he's saying--then what makes this a big moment?
What if it's an exciting speech that will completely alter the course of human civilization, involving high-level assassinations and altering the laws of physics as we know it? Maybe that's not very exciting to some of you, but to me and the kind of reader I'm writing for, it is exciting stuff
If you can write a speech that will "completely alter the course of human civilization" then what are you even doing here? You should be President of the world by now.