While one or two cards with Delve is probably fine for Eternal formats, what kind of world will it look like when we have access to ones that are more playable than Death Rattle
Decks pop off sooner and sooner with every passing year, and while part of that is due to the consistency and redundancy afforded to many archetypes through the sheer quantity of new cards being printed, a lot of that is tied to the Command Zone, and what is put inside of it
Evolving Wilds and Terramorphic Expanse won't accelerate your mana, but they will fix it
You can get immense value out of your little green friends in many different ways: you can destroy artifacts with Goblin Trashmaster, shoot down blockers with Pashalik Mons, or round up a new gang of recruits with Goblin Ringleader
Not a pure mirror, but one where your decks discard just plays into their plan
Its a decently powerful card that can wipe out a bunch of weak creatures at once and grows stronger whenever an enemy creature dies, though it doesnt exactly make for a top-tier commander