After all everything in the old GTA 3D era is 10% bigger than RAGE.
That has never been proven to be actually true.
The thing is, in the PS2-era, scale wasn't really a big issue. Go watch games from that era, you will notice a lot is out of scale as oppose to the real world. It's just how games were made.
Not everything is 'too big' anyway. Go check doors in any III-era GTA, some doors are too small, some too big and others are correctly scaled.
Scaling objects would also bring a big issue with converting, as you would need to adjust all the placement files, it's a hell of a lot work for basically no gain.