Honestly I disagree with that considering how out all of the toons today including legacy toons that are still around today only 0.7% managed to beat the
Aurum Vale which was a dungeon:
https://www.youtube.com/watch?v=OTi1hgiW_BU
and the title OP is asking for is just something you get for completing the
Battle for Aleport quest once:
https://www.youtube.com/watch?v=CHSi5tHwosU
Most of the toons from legacy that are around today mainly did Thousand Maws of Toto–Rak aka a level 20+ dungeon.
https://www.youtube.com/watch?v=hkK-j2er95g
https://www.youtube.com/watch?v=-i1TkmiJ_Kg
Now don't get me wrong as I agree that they should be rewarded for their loyalty and I agree that those achievements shouldn't be in the current version of XIV but based on the data of those toons that did stuck around the majority of them didn't invest much time into the legacy version of the product, infact a majority of them didn't earn over 1k gil. This means that those that did invest alot of time into it most likely deleted their toons or never recovered them, which is understandable as I did too. But if OP wants to earn that title from legacy then I say sure! let him! But
only if the Legacy version of the product becomes a playable product again and they earn it through playing through it like it should be.