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I think you're underestimating the power of a two-drop walker. Non-aggressive decks will be completely unable to deal with him on the play, and even then, if you play a creature (eg Vexing Devil that survives) on T1, then they'll still have trouble getting rid of him. He is still a strong engine on T2 that can produce high rewards for the right decks. Sure, random discard isn't great, but he is one hell of an accelerator for red decks - and that's definitely something red wants.
I agree that he probably isn't going to be game-breaking and he alone will not be responsible for putting RDW on the radar, but he will definitely see play - time has taught us that low-costed Walkers are generally very powerful, and so R&D likely tried to downplay him as much as possible for his casting cost. However, I think by virtue of being able to hit the field almost immediately, and still be hard to deal with into T4-T5 will make him playable and a welcome addition to some decks.
I think Tibalt is basically RDW's answer to Control decks - nearly unpreventable card advantage, combined with (basically) repeatable Sudden Impacts will hit control decks very hard - they can either keep their hand of removal and counterspells and take quite a bit of damage on T5 and T9, or they can be forced to play their hand earlier and faster, thus losing card advantage.
It's a very effective card for its cost, and its cost is what makes it useful. I'll probably be picking one up for EDH anyway, only because RWB needs as much draw power as it can get.