Being able to power out a turn four artifact that ramps, gains you life, grows your creatures, AND draws you cards is way too much
You won't get a traditional foil basic in this slot, and the eight new Commander cards and four Commander deck cards won't show up in this slot either
When the combo plan gets hated out, its often the Recruiter who offers a path to recovery, offering card draw, cost discounts, and incidental beatdown
There are plenty more that I think are pretty good cards, but don't quite cut the mustard for slots in this deck
The Eldrazi Titans can cost too much mana, and some legendary artifact creatures don't have a high enough impact on their own
This dude is such a key card I named the archetype after him