That failsafe has been inconsistent for a long time, including in TFA and the originals. One might also ask how much of a “gravity well” a large ship has - I mean, I suspect a “small moon” has one, but 60km of narrow flying-wing? Perhaps not.
Further there’s dispute over whether it’s a failsafe (and thus subject to being disabled) or whether, beyond a certain amount of gravity (or whatever), hyperdrives just can’t function. The entire universe is much easier to explain if it’s the latter - various “impossible” exploits of the Falcon can be down to it having its failsafe disabled (at least at times) and Han being a maniac, and yet interdictors (which are actually canon not EU thanks to one episode of Rebels!) still work.
I should also point out that the Guardian of the Lore (I forget his name) has discussed this, and said that it only worked because the Raddus is a bigass ship AND it was aiming at a large, hard-to-miss target (it still struck off-centre). Apparently only very large ships will impact in such a way that they cause massive destruction rather than being splattered.
Re: cloaking, AFAICT it was just a term for them suppressing the EM signals from the ships - something people have done IRL since the 1940s (it was confusion over such a device that lead to the crazy rumours about the Philadelphia experiment), and I don’t think that’s actually new to the SW universe. As soon as they realized the transports were there, they had no difficulty targeting them.
I noticed both also, and but it didn’t drop me out of the movie, I mean, I’m not sure why it would unless you automatically assumed there could be no reasonable explanation? Almost everyone I talked to about the movie had questions re: the hyperdrive (which they asked me because they know I’m an SW nerd).
EDIT - Btw apparently Snoke does have a minor backstory from some canon source:
None of it is relevant to the plot, which is presumably why it wasn’t mentioned.
We still don’t know jack about the Knights of Ren beyond that they’re ex-Luke’s Academy for sure (TLJ flashback) and that one vision of them in TFA.