So, I took a look at the commons in KTK. And I asked myself, what is a typical curve in this set going to look like?
First off, you want to drop a land on the first four turns at least. One of your two first lands should be the common dual. A one or two-drop creature, a morph or another three-drop, and a fixing stone should complete your first four turns. This gets you to five mana, representing one of the powerful common clan morph costs on turn five. Then, you can spare some time for tricks, raiding, removal, outlast, and so on.
Is there an aggro deck that can take advantage of such slow starts? Well, black can attack with a 2/4 common combo on turn two, there is a red haste bear, but that's about it. No good cheap combat tricks either, except for
Feat of Resistance. On the other hand, every clan can deploy a defensive one or two drop. And late-game cards just laugh at early drops - unless they have some +1/+1 counters and a horde of granted abilities.
The best early creature?
Disowned Ancestor. This can grow, can trigger raid without fear of dying, can block and kill pikers on turn two. All with a single color of mana. In fact, one of the few good things about early plays in KTK is that they all require a single colored mana. Again, making awkward starts less probable, thus further neutering aggro.
I like slower formats, and I like playing blue, so I might like KTK. But then, it looks like in the middle game, things can go wrong very fast for unprepared decks. So missing land drops will be lethal.