To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as a flashback cost), add any cost increases (such as kicker costs), then apply any cost reductions (such as that of The Earth Crystal's first ability)
The Gaffer Lifegain is already a popular theme among Commander decks, and The Gaffer easily slots into any of them
Also, the decks I said it didnt belong to are a narrow band (with the main relevant one being Najeela, the Blade-Blossom)
And you may get some extra shinies that you won't find in the Commander precons
But if you want to have fun and play something wacky then feel absolutely free to go above and beyond
In decks like Ad Nauseam + Tendrils, the card is used either to get enough storm count by drawing free spells or to find your Tendrils of Agony win condition