You can keep it for some sentimental value, but I don't suggest throwing away your etheric light by upgrading it. You're stuck with whatever perks you had when it was 300 attack and can't access the new ones. It used to have the highest impact tied with ice breaker pre-TDB, but after LDR came out with the same stats and Efrideet's and Black hammer had higher impact, it's obsolete now.
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They'll be plenty of etheric light to go around.