Well ki is hardly new, it came out in the mid 90's. With that being said, if it's one of your favorites then you should really try classic fighters because quite, frankly ki and ki2 only had a cult following at best. They tended to rip-off a lot of there gameplay ideas from another more popular series. (cough cough mk2 cough cough) And if tekken is one of your favs then that really shows how young you are. (And they are emulated in zinc btw, go play it and leave the mame devs alone) There is only one 3d fighter worth playing at this point and that's mkda because as you said it requires skill and more importantly, unlike other modern fighters that depend heavily on useless, mind-numbingly long "dial-a-combos" it's still fun. But I'm getting off topic here.
Why are ki and crusin so slow? Because the mame devs haven't optimized the code yet. It's as simple as that. The mame version of ki is only slightly more accurate than the u64 version. It should definately cut the framerates in half on most systems, but not by 10ths. The main reason ki was added at this point was to play with the new harddrive support.
Just be paitent, it will get there eventually.