2nd and goal at the 4 vs Bills Tomlin would have faith in the Bus to convert 100% of the time. Najee obviously not the case
Bettis ran with power everytime he touched the ball, always got the tough yards. Harris needs a full head of steam before he has any power, definitely not in the same league of power back like the bus.
He also didn't need to face a bottom of the barrel run defense in order to look the part or put up respectable numbers like Harris.
Harris averages 2 100yd rushing performances per season. it would take him 30 years to get to the 61 mark like the bus.
You cannot legitimately compare Najee Harris game to Jerome Bettis.