I also find it interesting that you chose 1978, which is probably the worst year for engine performance because of emissions regulations and it's affect on overall vehicle performance. So the smallest engine offered in the Jeep that year in a year that has probably the worst overall performance I would certainly expect that you'll see slow Jeeps.
After doing some of my own research though and looking more into performance data for earlier years, even dipping down into the pre-CJ7 years when horsepower still hadn't fallen off, I'm finding that the times still may not be enough to beat a modern fuel injected Jeep, in large part to a very peaky torque curve that drops off substantially before even 3,500 RPM. So I'm willing to concede the point.
However, that does not invalidate my overall point that I was trying to make.
And my point is that the Pentastar, while substantially better than the 3.8, is still not a great Jeep engine. It really does lack low end torque. Anything much below 2,000 RPM just doesn't give you much power. Sure, it cranks out a lot of horsepower at 6,200 RPM but so what? You still have to put really short gears in it to have any real semblance of crawling ability on anything very technical. I have 4.56 gears in my 2012 with a short 35" tire and I still can't get great control over big rocks to the point where I'm putting serious planning into a 4 speed Atlas. Those same gears and tires in a 4.0 Wrangler would perform a lot better in the big rocks because the 4.0 has better low end torque.