Alright, here’s some extra details about how Technologists do their thing.

While Technologists can create solid materials that are able to then indirectly alter intangibles (for example, the Steam Core is essentially an engine that lowers the vaporization point of water when the water's inside of it, allowing you to create steam without needing external fuel), they won’t be able to ‘gather’ those intangibles in the way that Dynamicists can. If the stone functions largely as a compression/storage device for light and sound (with sound and light released to activate certain effects), then it’ll probably take a while for them to charge up properly. But also due to this being storage, there’s no weakness to dark areas, so long as they’re sufficiently charged prior to this.

Specifically in regards to Egoism, you’ll probably have a whole religious culture/rite focused around indoctrinating the next crystal-bearers into the sort of self-focused mindset necessary to see their own body as a mutable substance. So that works well with this being a more traditional thing, especially because your nation has presumably been doing this for more than just the last 50 or so years. Larger crystals are needed if you want to do actual laser beams or sound cannons, smaller crystals function just fine as megaphones or flashlights, and each crystal will need to be Formulized for a specific function at a specific output level. A Technologist Polymath could alter the output on the go, but would need a fair bit longer if they wanted to alter the function.

It’s 100% viable for this light/sound-amplifying crystal to be the main industry of your nation too. It’s hard for me to really picture what madness you can do with a hundred million hertz, so I would say, because this is accomplished by distorting the laws of nature rather than by obeying the laws of nature, you don’t get that insane light-sound synergy. Still works for the purposes that you’d want, just no hard science implications behind it.

Also, easiest way of dodging around the 'bloodline ended because no longer human' problem would just be to like, have more kids.