Tiki is'nt that fast. Neither is his twin. ESPN has consistently used rankings that are more accurate to real life attributes and at the same time the rankings are less consistent. Overall the attritubutes in ESPN are a little shoddy. You see all sorts of wierd stuff like a 200 pound scat back with 65 strength (most of the OL guys don't have strength that high - another wierd thing). But, particularly with speed, they go by 40 times - Owens ain't that fast, and he is'nt in his game either.
Madden on the other hand has always seemed to give attribute boosts to star backs to make them better. No, Tiki is'nt very fast but his vision is excellent, has great balance, etc. As the user supplies the vision thing how do you make him a good back in the game without inflating his attributes? Think of Curtis Martin. At his age his attributes are not too hot, he's lost a step, etc. But he's still productive. Both games have tended to use break tackle as an equalizing stat - if you can't realistically get the overall rating of a back up to snuff just up the break tackle - maybe that's the reason broken tackles became such a problem in the 2K series.
I edit the attributes of many backs in 2K. I ignore the overall ranking while editing and let the chips fall where they may. I reduced Michael Bennett from 93 to 85 by lowering his break tackle attribute. His speed I raised slightly, because 2K uses his 40 time from the combine when he had a pulled hamstring. He does'nt break many tackles for me but the long runs he gets keeps his average at about 5.1 - and this is what his career average is in real life.