It is, but as noted, having one in your "opening hand" 100% of the time is a big difference.
Also, while Power Artifact is cheaper and blue, this guy is not prone to 2 for 1 removal on your artifact. If your Monolith gets nuked in response, you don't have to find 2 more pieces to assemble the combo again.
Also now you can run 8 Monolith and 8 reducers if you want, making the combo very easy to assemble without tutors.
So this is a very reliable way to have infinite mana with Grim Monolith.
The casting cost is as bit annoying, but it shouldn't be that bad to get out consistently.
The deckbuilding restriction isn't too bad as you can still have mostly instants and sorceries. It does however prevent you from playing Young Pyro and Mentor, but you can play all the Planeswalker you want.
As a side note, I know they needed to give it some kind of activated ability, but the no block thing is just so out of place on there.
Is it me or that is a very agressive sideboard card for Vintage? Against a lot of decks, it would create easily 9 power at instant speed. One green also means it's very splashable in artifact mirror matchups.
Instant speed means you can just play a more control game and slam this EOT or whenever you find an opening.
If you're casting this before going off, you're going to cast 6-7 more spells, so lose 6-7 life. If you fizzle, you're most likely just dead as you don't get a second chance. You'd need to run more bounce spells than usual to mitigate that.
For that much life and mana, I think I'd rather cast Infernal Contract, it's better in multiples and you know the cost when you play it.
Also, the artwork makes me think of Michael Jackson.