It is straight-up said that the industrial mech factories used similar technology and equipment as the battlemech factories. That is why industrial mechs are so rare until the Helm Memory Core is distributed. It even says that the factories were stripped to get battlemech factories running again. That is the lore of the Industrial mech I am not assuming anything. I am simply telling you what is the information that is given.
Btw, by the provided tech levels I was thinking of them right lol.
IndiMechs are NOT rare though . . . filled one of the early books (GDL novel), we have TRO VA that describes ones that were existed or built through out the Succession Wars.
Ceres Metals is building the Guard Quad SecurityMech and in enough numbers to export to the DC by 3028.
Alshain/DC starts building the Pacifier in 3031
Coventry was building the CPK-19 since the Star League
Duran exports the Cattlemaster which was started in 3024
Terra produced the Carbine construction mech in 3028
Crosscut series of ForestryMechs, a new Demo model was introduced in 2910
The Buster LoaderMech had 20 different versions produced up till the 21st in 3060, from 15 onward no functional differences till 21
Dig King started in 2571 on Archenar and was produced with variants until replaced by the Dig Lord in 3057
Furillo developed and produced the Lugger SalvageMech before 3050
Scavenger SalvageMech that was built into the Succession Wars ended up armed at various times
and there are more . . .
No one is suggesting Mechdur is Defiance-under-the-Mountain. What we are suggesting is that since they build- IN FACTORIES- mech spec armor and mech scale weaponry- btw their own armored vehicles too!- the components (myomer, ICE, commercial gyro, commercial armor, commercial structure, commercial cockpits) with maybe some being imported and then assemble them by hand (really just verbage for labor intensive) with some mechanization. Its not the completely automated Valkyrie factory on New Avalon that churns out hundreds of light mechs a year during the timeframe. Perhaps one or two a month, which is truly dependent upon the feeder production lines (commercial gyro, ICE engine, cockpit being the critical 3).
The simple reason the production site was never interrupted? It was not worth the effort by the Houses or other neighbors. If the IndiMechs are not built by any sort of automation, there is nothing worth taking.
'high tech' AC IndiMechs could have-
Std Internal Structure (used in the 4 vehicles they build)
Std/mech spec armor (clearly said to be produced, used in vehicles)