If one runs the numbers, the 757 typically has higher thrust to weight ratios than other 121 a/c...the 717 and MD90 are in the same ballpark.
If one compares a DC9-30 w/ a 717, the wing differences are minimal...but the thrust to weight ratio is greatly increased in the 717 as compared to its older brother. One could have made the most comprehensive change to the DC9 wing possible; but if max gross weights and thrust were held constant, the climb performance wouldn't change nearly as significantly as is has with the higher thrust engines of the 717. Climb performance is largely a function of excess thrust.
Also, the 328 jet is an excellent climber...corporate jets and fighters have engines near their centerlines for a couple of big reasons...for fighters, it keeps the size of the vertical tail(s) to a minimum in case of a failed engine. For corporate a/c, engines slung under the wing force raise the profile of the a/c up far enough such that just about anything that needs to be done on the a/c from daily maint to loading pax would require ladders or larger airstairs than typically used, which detracts from the mission flexability of a corporate a/c at remote airports.