> I don't know if I'll try rewriting the first chapter, I'm just kind of relieved to finally move it out of the WIP folder after two years.

Good point. That's why I was saying maybe you shouldn't have tried to explain every detail of the setting to the newcomers, and instead focus on what's different and important in your own story. Maybe that wouldn't have taken two years. But what's done is done, no point in turning back now that you've finally gotten done with the prologue and got to the actual story. I bet no reader would prefer you reworking the prologue for another two years over seeing the continuation hopefully soon.

I may be wrong judging from just one chapter, but if your story is going to focus more on Servants killing each other in various ways inside Chaldea for the sake of power ups, rather than on saving the humanity, then the original story events can be skipped entirely and just mentioned like "after the events of such and such singularity such and such servants have joined Chaldea… so let's see how we can have fun with them now", or maybe a character telling another character "remember how you've used such and such technique in that battle back then? Wouldn't it be fun to try use it for fun?" and readers familiar with the original story would be pleased with recognizing the reference, while for readers unfamiliar that suggestion by itself would serve as enough introduction into that character having that technique.