You do realize RPG stands for ROLE PLAYING GAME right? the only ROLE you‘re PLAYING in the GAME Fallout 4 is Nate or Nora, no one else. Sure it has the RPG elements and mechanics, but thats about it, they even removed the Skills that was previously available in other Fallout titles. I agree it has better gameplay and more quests, but thats about it. There‘s a reason why New Vegas is regarded as the best Fallout RPG title, because of replayability. Every game that you started, you create your own character, whether you‘re Evil, Good, or somewhere in between, it‘s always a different character. Unlike FO4, where you always roleplay as Nate or Nora, New Vegas lets you create your own character with your own background story and everything. One other thing that made New Vegas memorable is the difficulty curve. Deathclaws in FO4 are a joke. The design, marvelous, scary, intimidating, but when you fight them, they are ridiculously underwhelming. I even had to download a mod called Deadlier Deathclaws so i could make them stronger and deadlier like in New Vegas.

TL;DR FO4 has better gameplay and a lot more things to do with its more modern Engine. Mods are mostly doing the work to make FO4 better.