The artifact density at common is the whole question, and the honest answer is that TMT does not feed this trigger the way the printing suggests. Donatello grows when an artifact enters the battlefield, not when one is cast or equipped, and most of the artifacts at common are Equipment: Bespoke Bō, Novel Nunchaku. An Equipment cast before Donatello is down, then equipped after, puts zero counters on him; the equip is not an ETB. Food tokens count, the utility lands do not. So the growth rate that makes this a build-around lives almost entirely above common, in the token-makers and artifact creatures at uncommon that actually enter the battlefield and can chain two or three in a turn.
That places it firmly in UR Artifacts, the only supported pair drafting those uncommon ETBs in volume. There the body comes down P1P4 to P1P6 once you have committed to the artifact engine, and the pick climbs toward P1P3 after a couple of token-makers are already in the pile: a four-turn evasive clock that the deck can build around. GU, the other blue pair, treats it far worse. The green half wants ground bodies and trample, and a 1/2 that does nothing without an artifact subtheme loses the slot to a creature that blocks.
The punisher is Grounded for Life. White's removal is cheaper against a tapped creature, and an evasive attacker is tapped on the turn that matters most. Protect the first two counters and you have a real threat; the engine that gets you to the seventh almost never assembles in time.
