The issue is that the floor of the card (when its only making three or four mana) is still way too high, because Dockside is a card that can be looped, reanimated, flickered or cloned to such a degree that simply making an extra treasure or two is still enough to win the game
The times where you have the mana to pay for his ETB are going to be limited I think, but he's a really nice draw engine for a proliferate deck
"Well you still have to pay the mana cost, and it's instant spells only, how bad can it be?" It means you can draw lots of cards with Brainstorm, blink Chun-Li to get her out of harm's way with an Ephemerate, or make your board untouchable with a Teferi's Protection every turn
Its a mix between a bear and a Chromatic Lantern, while it turns even a 1/1 ally token into a mana dork
Well yeah, it's artifacts, of course it's all gonna be fast mana and the like