Yeah but if you need to solder in a musical instrument tube amp, you can do it with a hot brick. Casual home tinker types can manage pretty OK on point-to-point stuff.

Fairly good, modern SS amp (like Boss Katana) have complex circuitry that requires a very knowledgeable tech who can diagnose and repair the issue. That can be $$$/h. Repair can cost as much as the amp. Guitar tech amp about repairing Katana: https://youtu.be/EPvon7zLdgw

That's because the manufacturer won't provide service manuals or schematics. Probably the thing itself is not designed to be repairable, but that's an issue with the product itself, not with the technology.

exactly this, and it sucks to throw stuff out because of this. I'd rather pay twice as much for quality and not create junk and support the junk economy. I'm done throwing out gear.