V8 will probably out tow it, definitely out last it, and it wont lose much MPG compared to the V6 when towing. IMO V6 in full size trucks is silly unless you dont plan on using it as a truck much. 

A naturally aspirated V8 with fuel injection will pull more reliably and for longer term than the turbocharged V6 that has similar performance. It won't have the lower-end torque the turbocharger provides, but there are more cylinders producing power per revolution of the crank, and you're not ramming as much air as possible into the cylinders, saving what will ultimately be extremely expensive wear when the time comes. Compare the torque values in the individual engines' power bands to what your use requires. A naturally aspirated engine will have its power band higher up in the RPMs, which is what you want if you're driving on the highway. If you're also going off-roading and rock climbing, etc. you need high torque at lower engine speeds, then a turbo would be better suited. 

GDI and typical fuel injection also have an impact on this, but for demonstation's sake, compare the 2.3L EcoBoost with the 3.7L cyclone V6. the 3.7L V6 puts out 300 horsepower. It peaks at 278 pound feet of torque at 4,000 RPM Compare those numbers to the EcoBoost 2.3L, which puts out 310 horsepower and 305 pound feet of torque at 3200 RM. They're comparable, but the torque rating at low RPM is higher on the 2.3L than the V6. 

Personally, I'd go V8 because they're simple, tried and true. I won't buy a truck if I'm MPG conscience. They're going to be gas hogs if you use them for what they're for.

Turbochargers are for going fast. They are weak in the low end.

For towing you need raw TORQUE. Always go for the bigger displacement engine.

Contrarian view:

Here's the thing:  You aren't just choosing an engine, you are choosing the whole package.  The choice is between an old truck with a solid V8 and a new truck with a probably-solid-but-who-knows-yet turbo V6.

No doubt, the V8 is gonna tow a lot of pounds for a lot of miles.  But the 2022 has a higher tow rating because of the upgrades in frame, transmission, suspension, and brakes.  The new truck is going to be much more stable at high speeds and will stop much better than the old.

If you are towing a mid-range weight (5000-8000 lb or so), it probably doesn't matter because they both can tow that with a good safety margin.  But if you are at the upper end (9000-10000 or more), the 2022 will likely give you less drama.

Or let's be real, inventories are so low right now that finding either a new-2021 or 2022 will be tough.  Take what you can get.

How much does he want to tow?

Gotta stick with a V8 with that big of a load. I would also make sure it has an excellent transmission cooler and I would change trani fluids much more frequently. BUT again check the Mfg tow ratings and go from there.