It's like they didn't even care for the rules or reason of anything previously established---what the heck is "hyperspace skipping" and why does it matter, it's never mentioned again in the movie (so it's not even a heavy-handed setup for later, like I originally expected). Hyperspace jumps now happen between places instantaneously or nearly so (confusing the heck out of the idea that hyperspace travel takes time as presented in, say, literally the first-ever Star Wars movie), can happen in atmosphere and in a gravity well (yeah, Rogue One did that as well, but still, really?) Why bother using regular engines if you can hyperspace yourself everywhere, from any point, at any time? Why, precisely, can First Order TIE fighters
The "Holdo Maneuver was a 1-in-a-hundred-million shot" thing is a patently ridiculous attempt to cover up the problems presented by using hyperspace as a weapon, since if you just go grab a thousand asteroids, put a thousand hyperdrives on them, you could then jump back and forth across the system until one of the things explodes and the entire fleet is just instantly killed. Even if you've got to make a hundred thousand jumps, since hyperspace jumps now take only a couple seconds you could definitely jump back and forth enough to kill that fleet within the time limit of 18 hours or whatever, even if the enemy detected you in the process they'd evidently take too long to actually deploy to matter, especially if you dropped at asteroid at high speed out of hyperspace pointed directly at the beacon tower things (why can you not just
check the direction of gravity to figure out how to launch this fleet?) and just let Sir Isaac Newton finish *that* job for you.
They should've had it be a bunch of droid-crewed/slaved-together ships like the Katana Fleet in the old canon because that would've been cooler and more reasonable and given a sort-of-possibly-maybe-not-really decent explanation for why they need some sort of activation signal or whatever, to suit Palpatine's desire for ultimate control over everything (and his probable pathological hatred of any and all possibility of rebellion, given what the last Rebellion did to him
).