He wasn’t a scientist he was a low level technician.
He didn’t even finish high school completely (no diploma), and dropped out of his engineering course at uni.
https://en.m.wikipedia.org/wiki/Mordechai_Vanunu
While he did revealed some information a lot of the technical details he talked about during his early interviews made absolutely no sense.
He was imprisoned on the basis of revealing classified information and taking photographs of a sensitive site.
Whether Israel has actual assembled weapons or not, they are a breakout state they have 2 reactors one at Dimona one at Soreq and even if in the 60’s and 70’s they didn’t had the knowledge to build nukes considering they took in nearly 2M Russian Jews and their family members they probably could’ve gained that capability from that immigration since the late 80’s to early 90’s.
Israel can also potentially posses a nuclear Triad however for Israel nukes are only really useful as a deterrent against a conventional threat as due to their size MAD will not work for them against any of their possible opponents in the region.
MAD also requires that everyone in the equation will be sane and held accountable, if there is an Islamist coup in say Pakistan or if a regional theocratic regime gets nukes it’s not clear how MAD would work even if the geographical and population sizes weren’t that different.