"... from all colors"? Oh, that is just nonsense; will play out like unblockable 2/2 with indestructible. Colorless mana isn't that hard to come by.

Think turn one City of Traitors (which obviously is bonkers, but still) into this. What is the opponent supposed to do?

Reminds me of True-Name Nemesis which is just disgusting.

I think it's fine. Ignoring that protection isn't used anymore, it's 50% weaker than TNN for one thing. For another, it's pretty hard to have CC available on turn two unless you're playing mono-colorless, which is inherently restricted.

How is it 50 % weaker? It even has a lesser CMC and more toughness (making it more resistant to Shrivel effects). Pain lands, such as Adarkar Wastes, make it rather easy to play stuff like this on curve.

A lot of this really depends what kind of lands are you about to provide in the set, but in Modern/Legacy this might shake things up.

That, and I would like threats to generally have reasonable answers to them - not just being countered or the board being wrathed.

2 power instead of 3 power means it takes 50% longer to kill an opponent. Plus it doesn't have tribal support.

Hitting 3 damage per turn takes someone from 20 to -2 in seven turns. Killing someone with 2 power creature from 20 to 0 life takes ten turns. So it's around 40 % more efficient. Still, you can likely drop this on turn two instead of turn three so that argument is kinda null.

You're right about the tribal support though.

In any case, even if it's slightly weaker (which is arguable IMO), it's not much better to be a slightly less broken version of a broken card. For example, many of the so-called "fixed versions" of Timetwister and Black Lotus have been banned in various formats.