Well that just isn't true. There have been people who have tuned out AFM with issues and people with AFM that never had an issue (most are the latter) it isn't going to magically make it more reliable tuning it out, there is zero evidence of that just internet theories that don't consider the other side of not having it work. I am starting to think that tuning companies or those that work for them are behind this theory. There are so few that have had issues with AFM that should be zero concern, there are millions of those engines out there and failures are minimal (in the decimal percent); it is a machine built and assembled by people so there will be rogue failures, nothing to scare others about.
The better mpg wasn't because of the AFM being turned off but tuned to be more efficient, if you had it tuned how it is now and run AFM you would be getting even better MPG. AFM does save mpg over always running on 8 cylinders no mater which way you slice it...
Finally the oil consumption is mostly attributed to early LS 5.3 architecture and the piston rings used, 2014 in the redesign to LT architecture those were changed as well as many other parts and designs and not much is out there about any oil consumption now. People tend to hang on old issues and think they apply to new ones and that is not the case. Just like the valve build up, that was from early adapters of direct injection, most new models it is minimal as they have learned how to handle that side effect, but people still think it applies today and their valves are going to look like an early 2000's VW or Audi...
OP, don't worry about the reliability of the 5.3, stock it will most likely last you a very long time with proper maintenance as it is the most widely used. The two newer motors (3.0 and 2.7) should as well as they do so much testing and validation on them both in real world and with computers. My buddy had a pre 2014 Tahoe with the 5.3 and AFM (2012 I believe?) that went nearly 300k with out issue before trading it in, he drove a lot for his job and these newer gen 5.3's are even more reliable.
Tyler