Agreed, these procedures are practical for small automobile dynamic engines with proper procedure along with removal of some parts and not the complete cylinder head or complete engine.
Same thing is done on big stationary industrial diesel / HFO marine engines as part of preventive maintenance periodically as we also have patent Diesel labs having equipment for Inj pressure testing/ cal and pump testing / cal machines, but by the time in cylinder heads heavy carbon build up occurs, the valve sinkages already got out of spec so complete cylinder head has to be removed for rebuild.
In bigger ( industrial) engines maintenance procedures becomes a bit different and some prime parts removal is inevitable at certain stage.
We are on the same page technically that some things ( as per OEM recommendations only) can be done but not the complete internals especially the bottom end side and especially without removing any thing.