Not sure I understand the nerf to Graboids.
Mono-life is just as fast AND has healing.
Mono-fire is just as fast AND has incredible permenant control.
The only thing Earth had going for it was graboids and they required 2 elements in order to play.
In fact, if you play Top50, you rarely come accross a deck using Graboids however, you WILL come across mono-Life and mono-Fire decks. Further, those pure mono decks very often beat my upgraded Graboid deck.
The only reason I use the Graboid deck is because it uses Mark of Time which synergizes with my Mark of Time Rainbow. With this nerf, I'll just switch to the already superior mono-life or fire and just have to suck up the 100 electrum to switch marks.
This game suffers from a disturbing lack of deck diversity and this change will just make this worse.