I was still active duty when the Hummer first came into issue. I had my reservations but after the usual shake down period with the troops (hardest testers in the world) the vehicle proved to be robust and reliable.
The fact of the matter is, was, and will be that the chassis was designed to carry a specific amount of weight plus a factor for crew/cargo.
Up armoring the Hummer overloads the design specs by a large margin. With armor they have to be air conditioned or the troops suffer heatstroke and that leads to other add ons like a bigger aternator.
Pushing the design specs by up armoring results in a much slower vehicle which will never reach as built lifetime due to the severe weight load. Newer Hummers that have factory added armor and such are beefed up to handle the increased load.
The original Hummer was designed as a replacement for the M151 jeep nothing more nothing less. Protection in a jeep was based on speed and manuverability. The up armored older Hummers have neither.
You are correct that the factory modified M1114's are 'beefed up', but not nearly enough. They still have all sorts of problems associated with weight. For instance, tie rods. When turning a vehicle that heavy, especially under speed, the tie rods buckle. The original M998 tie rods didn't stand a chance. So they are 'beefed up' but still far less reliable than the orginal M998.