Possible, but the Landsraad may have decided a regime change was in order sometime down the line. And much like Shaddam had his back to one wall, Leto might have found himself with his back to another. And it's not like "oh surely he wouldn't do that" is a great comfort to those who are in power and fear losing it
I get what you mean, but that's not usually how literary analysis works. The intent of the author isn't usually a concern - for one because we rarely know it, but also because the author - as you say - may not actually have consciously intended certain things that still ended up happening. Art is a creative process, and while it often involves a lot of thought, it rarely involves the amount of thought that is put into it after the fact by interpretation. It's the proverbial "why is the door red?" kind of deal, where the author might simply have intuitively chosen the door to be red, but thorough interpretation and critique can come up with very good reasons why it HAD to be red; even though those reasons might never have been conscious thoughts that the author had while writing it.
That's what I mean by conversation ender - it's a silver-bullet statement that can shut down any discourse because ANYTHING is just "machination to tell a story" and as such it's not very useful. It's basically like saying "yeah okay but none of this is real, it's just words on a page" - 100% true, but also totally unhelpful to any attempt to discuss a story
(full disclosure, I am a literature professor so this is kind of what I do professionally, I don't mean to come across as condescending)