doesn't have to be INS to have DME /DME etc.
Most Turbo props won't have INS and alot of the regional jets won't have either. So no map shift, you can get the difference between GPS position and DME /DME derived if you go through a few pages but the unit bins the gps position if there is a conflict and goes with DME/DME.
Alot have the Honeywell GNSX type of kit which have various different features depending on the mode.
Its not really a FMC because although it can do certain fuel calcs and can have an input from the fuel flow, not all do.
I am sure there are far more fancy pieces of kit in the GA world.
The idea that the world s commercial aircraft are flying around putting all there trust in GPS is rather stretching it. Its a tool but most of the time it comes down very low on the list of Nav data. Hence why there really isn't that much of a push from commercial operators to have GPS approaches. So there is no one to pay for the surveying and production which is why nothing is really progressing on that front.