Single Mana legendary cards are great from rebellion rewards. I think with the time when we wil be able to upgrade them, then it will be useful as most of the single Manna legendary cards are with attacking abilities..
You are a bit lucky guy pulled two legendary from 50 major chests .
In every season I able to take my Glint tokens over 100K, but there is no legendary till now.
By the way Arachne Weaver is great card with Corrupted Healing ability.