Sorry, but this complaint is a pet peeve of mine.
1. Don't confuse New Vegas's DLC Weapons with Vanilla weapons
New Vegas had a metric crapton of weapons added in DLC. It's not really fair to compare vanilla Fallout 4 with GOTY edition New Vegas.
2. Named weapons and Recolorings don't count
Named weapons with only slight diffrences in appearance and stats shouldn't really be counted as different weapons. I guess it's more fair if you count all the named weapons from both games, but people don't seem to do that.
3. The biggest one: The New Vegas System is completely different because it counts varaints seperately.
Let's look at submachine guns. Lots of people say that Fallout 4 only had 1 submachinegun compared New Vegas's 3:
FO4
-Submachinegun (Thompson)
New Vegas (base game)
-9mm SMG
-10mm SMG
- .22 SMG
Seem's like a gap right?
Well, not really. You see, if we compare the two on the same level, the FO4 actually has the same number. Why? Becuase auto pistols are classified as seperate SMGs in Vegas but as pistol derivatives in 4, even though there's no practical difference. So our list should really look like this:
4
- Submachinegun
- Auto 10mm
- Auto Pipe pistol
Vegas
- 9mm SMG
- 10mm SMG
- .22 SMG
But what about other weapon types? Well, again, this is because what 4 qualifies as derivatives, Vegas would qualify as seperate weapons. Let's take, for example, the double barreled shotgun. In Vegas, the DB shotgun and the sawed-off DB shotgun are classified as seperate weapons, but in 4, the sawed-off is a derivative of the full DB shotgun.
Another example: bolt-action rifles. In New Vegas, the hunting rifle, scoped hunting rifle, and military-grade sniper rifle would all be qualified as seperate weapons. In 4, they (in addition to the sawed-off hunting rifle) would all be qualified as hunting rifle derivatives, even though, appearance and stats wise, my Scoped Ported .50 Sniper Rifle with a Marksman's Stock has little in common with a Short .308 Hunting Rifle.
Really, all the full-auto mods would be seperate weapons under the New Vegas classification. A Revolving Pipe Sniper Rifle and an Automatic Pipe Rifle would've certainly been seperate weapons under the New Vegas system (and yes, I know they're not actually in New Vegas).
TL,DR: In Vegas, every derivative would be classified as a seperate weapon, especially the ones that change firing mode or ammo type. Therefore, New Vegas actually doesn't have nearly the leg up on 4 people think it does.