Lord of All Hopefulness is modern (around the 1960's or so). As mentioned above, Be Thou My Vision IS old - a 7th or 8th Century Gaelic poem. Translated by Byrne and versified by Hull, the tune was only added afterwards - possibly for the "English Hymnal" collection which used a lot of traditional tunes, fashionable in the early 20th century when the intelligentsia were trying to bring about an English Revival.
Yes, I DO know that BOTB is Irish-collected and not English, but the posh people of aound a hundred yeasr or so ago weren't too certain - "traditional" was enough for them.