Rangers can use a Longsword.
The longsword is a "Versatile" weapon.
Versatile weapons can be used with one or two hands and deal higher damage (d10 in the longsword's case) when used with two hands.
So, Aragorn charging into battle with Narsil is...there. It's done. Spears, staves, battleaxes, war hammers, longswords layin' the smackdown using two hands. If that's the "archetype" image you're trying to achieve, you have it.
Why does the Ranger need something added to it to give you this?
They also can already use "Heavy" weapons, because heavy weapons are Martial weapons. So if you want to say "But Narsil's a two-handed sword" (it isn't, but if you want to argue it is) you can use that sword already, as well. Or a glaive or halberd or whatever. It's just not, understandably, one of the things Rangers, as a class, prefer enough to warrant a mode of "fighting style." Other ways of combat are more effective and keep with the flavor of the class.
But hey, do i think it will "break" anything? No. If it's something you want in your game and your DM says it's ok, then who the heck am I? My opinion is completely irrelevant.
I, personally, would see no reason to add this to/ask this of the ranger class if I wanted to play one. And would I add it in, if requested as a DM, for a particular PC?...Probably...and follow the DMG suggestion that, by virtue of that addition, a different ranger ability would get removed. But I would not just alter the class as a whole for this...admittedly narrow, if not singular, image of how someone charged into battle...not even in the neighborhood of a "trait", let alone "iconic" or "archetypal."