Why would he ever consider a 4L70E? Aren't they the same case length as a 60E? At that point he's swapping transfer cases and/or driveshafts to go to a weaker transmission than he already has.
Because it's a drop in for the 4L60E, which everyone thought he was talking about until he clarified which makes both your points just you not missing a chance to be a dick.
Also, GM themselves recommends the 4L70E for a lot of hot-rodder type applications because it is a modified transmission designed for higher horsepower applications. The 4L70E is lighter and smaller than the 4L80E and has gear ratios that some people find more appealing than the 4L80E. The strength and power handling improvements made to it eliminate all the reasons not to use a 4L60E with the advantages and lighter weight that it may have for some users.
The 4L70E has a torque rating of 495 lb-ft while the 4L80E is rated to 440 lb-ft.
The 4L70E has the following gear ratios
1st: 3.06, 2nd: 1.62, 3rd: 1.00, 4th: 0.70
The 4L80E has:
1st: 2.48, 2nd: 1.48, 3rd: 1.00, 4th: 0.75
SO I assume even you can grasp that the lower first gear and higher OD gear make the 4L70E a better transmission choice for trucks that want a good crawler low gear and a higher OD gear for decent highway cruising and fuel economy.