Did you play FO3 on very hard as well ?
It was probably the hardcoe mode that slowed you down in FONV .
I personally think FO3 has a bit more content than FONV . Because FO3 definitely felt longer to me .
I don't recall to be honest. I think I started FO3 on normal and then increased the difficulty later.
FO3 was the game that sort of re-introduced me to gaming after about a 20-year hiatus. I really liked the game, but after looking around for some FO3 mods on TESNexus, I discovered Oblivion and there was something about the game world, even the vanilla version, that lent itself to roleplaying and exploration in a way that I didn't experience with FO3.
For me, however FNV provided a lot longer playthrough than FO3, even though I had DLC for FO3. Maybe it was because I used fast travel in FO3? The metro tunnels were kind of annoying to navigate, so I used fast travel.
I don't use fast travel in New Vegas or Oblivion.