Deep core mining didn't recive a nerf, neither did laser mining, except for Painite, that payed way to much.
EDIT: I should say that Low Temperature Diamonds also got a nerf in price. Both LTDs and Painite can be both laser mined as well as Core mined.
Nowdays, when it comes to laser mining, Painite, Platinum and Osmium are well worth mining; makes the mining run go faster. I personally mine Gold, Silver, Osmium, Painite, Platinum and Palladium. It's free money, and... above all, Painite prices got nerfed, but the rest got a HUGE boost.
When it comes to Core mining, Void Opals might still be the best, but most of the Core-only mining minerals are close to a million and above it. The market fluctuates a lot with these, so there isn't just "one" ore that is worth mining...
The number one thing holding Core mining back is that the Pulse Wave Analyzer has been broken for a couple of months. News are that FDev will release a fix for this on the 16:th of December... tomorrow.
Do yourself a favour and go to Inara and have a look and see on all the mined materials.
The community site for Elite: Dangerous, Starfield, Kingdom Come: Deliverance with the game databases, information, gaming news and other handy content...
inara.cz