Disagree, at least based on Skyrim. I played 700+ hrs of Vanilla, and only used a single mod (ie; No More Blocky Faces), and was content.
Then I started to watch Gophervids, and became emboldened to try a Mod Manager and add even more mods to tailor the experience. It certainly can enhance the experience, but the original is what I sought to preserve as a rule; not change.
Different opinions then. However, I doubt I am alone in this thought process, since Bethesda's unofficial motto seems to be "Mods will fix" and with mods coming to consoles now, this rings truer than ever.
I could never play Skyrim without a complete texture overhaul, ENB, lighting/weather overhaul, swords and bows remodeled, immersive armours and weapons, werewolf/vampire overhaul, audio overhaul, new weapons and armours and the mod that brings them all together, Skyre. Sames goes for FO3 and F:NV, with their respective FWE and PN mods.
I'm actually thinking of reinstalling Skyrim now, seems like T3ndo has given up modding for now, which sucks. Hopefully an equally talented modder or team can overhaul FO4, just as they did once for FO3, with FWE.