The weight to size to power ratios mean very little. Consider the wide cubic inch variety of a small block Chevy 283 to 400 cubic inches. The range of factory horsepower from the same basic block configuration.Same applies to many manufactures engine lines. Opposite end of the spectrum consider the 5.9 Cummings medium diesel in the same ratios.
I do favor the 2.7, think it an very strong and potent power-plant, but consider the original post caparison fairly meaningless. KM

My experience was nothing but great with the 2015 2-7. 48k miles and zero issues and peppy as all get out. But I am torn between a 2-7 CC 5/5 and a 3.5 CC 6/5.

IMO the comparison is woefully incomplete. It only gives the result of the differing designs without delving into the implications. For a true comparison I'd be looking at things like bearing pressure per square inch of bearing area, cylinder pressures, piston speeds, rod ratios, and so on. While I'm a fan of the motor in general, a true engine comparison needs to take into account the amount of stress and structural headroom in the design. This is especially true when dealing with a truck motor where a lower stressed engine is more desirable.

To the OP, why did you feel the little, small 2.7 needed any "defending"? I sure don't feel like my 5.0 needs defending.

And the dick swinging contest continues...

My biggest concern is durability, which seems pretty positive so far.

It's an age old problem, across the spectrum of nearly all industry: How do you get more power out of smaller and smaller motors? The question applies to cars and trucks, tractors, and drones. Cameras, printers, and lawn mowers. Everyone seeks the most satisfying power to size ratio, and the limits are constantly stretched, surpassed, and somewhat limited, just by the simple power limitations that physics define.

In other words, just like other trucks I've had:

I'll just drive the wheels off of it.

After owning a 5.4, I had absolutely no confidence that Ford can build a reliable modern V8. I've had turbos before, they don't worry me near as much as Ford's variable valve timing systems. A worry well placed, if other threads are any indication.

2.7 is cheaper, more available on the lots, and returns better economy than the 3.5 or 5.0 while being nearly if not just as fast. No need to defend it, it's best in class by a mile compared to the competition. It does come with limited payload and towing, but that's where the other two come in. Choices are a good thing, each engine has its strong points.