tekken looks kinda shitty when you take a closer look on the cloths animation, hair and skin of the chars.

Well because its Tekken Tag the game needs to hold 4 characters in memory. You just won't see the same level of detail and fidelity as Soul Calibur. Of course if this was a Wii U exclusive and built form the ground up for Wii U then they could have taken advantage of the extra memory.

true story bro, but when you look at ninja gaiden, there are also a lot of characters on the screen. the enemy models are quite good and the game should also have a high fps rate, as i can tell from gameplay trailers.

Developers will give priority to different things. For a game like Tekken, the focus would be on smooth, snappy animation, plus there's a lot of data in the background governing hit boxes, hit-stun, super armour; all the important things that go into a fighting game.