The more interesting repairs people like Rossman, ipad rehab, and others do can involve IC replacement or circuit trace repair and some of their complaints around sourcing ICs, not just larger assemblies like a display.
This also flows into expertise and tools around such repairs - you need some knowledge of the PCB schematic (in which there's a cottage industry around selling them like http://www.laptop-schematics.com/ ), how to use board rework tools (you need more than just a soldering iron). I sorta dream of a prosumer 'makerspace' for people to do these things but in practice feel like anyone with these skills just asks to use their employer's lab in the off-hours for such things or tends to their own private homelab.