The power comes from the card selection
As for life gain, it can only recover 1 point on its own, but it can be sufficiently utilized within Green alone
Even without stacking a ton of spells, being able to tutor one dragon straight onto the battlefield is powerful but when you storm off, you could end up putting three, four, or even five dragons into play all at once
With a haste enabler, like Lightning Greaves, and a way to untap creatures or generate mana on death, like Pitiless Plunderer, you can create an infinite loop of Joo Dees, filling your graveyard with the Surveil trigger
I find them super comfy to shuffle and play with
In my time I have made a lot of Smokestack decks with a lot of different themes, some even without the clunky Smokestack