6.4 SRT Jeep GC can tow 7,000lbs no problems, as can the 5.7 Jeep Grand Cherokee.
Yet the 5.7 runs dramatically richer.
Same thing when both engines are in a Challenger.

If you dont believe me download HP Tuners software and look at some standard files. You can see under Power Enrichment above 4250RPM the 5.7 is heavily richened compared to the 6.4.

Also note that the Ram 5.7 made more HP than the car 5.7 as 5.7 was the only engine option until 2014 when they added the 6.4 BGE