LiFePo4 Lithium batteries and there support hardware (DC-DC chargers and solar controllers with LiFePo4 charge profiles, etc.) are a quickly evolving technology. Having said that I have been watching it somewhat closely for the last 5 years or so, and decided that it was mature enough to make the jump to about 6 months ago. It is hard to know for sure, but I get the feeling that things are beginning to stabilize and mature in the market, particularly in the form of so called drop in batteries.
Think of it the way flat panel TV's have evolved over the last 20 years or so, I remember seeing my first flat panel plasma screen TV at a trade show in 2001, it was 36 inch screen and cost $30,000 with I think a 640x480 resolution, a year later they were down to under $10,000 and had 720P resolution, by 2007 I bought my first LCD flat panel TV, a 35 inch model, which was not really flat, but about 7 inches thick, and the picture was not all that great, 7 years later in 2013 we bought our next flat panel TV, this one was 42 inch and 1080P and we still have it today, our latest flat panel TV is a 50 inch model bought 7 years after that in 2020, and other than weighing about half as much as the 2013 42 inch TV the picture is not all that different, sure it is better (slightly sharper, brighter colors, etc), but not that dramatic difference I saw between the 2007 TV and the 2013 model, a difference so great that the 2007 unit was relegated to the storage closet, and not even the guest bedroom.
To relate this to LiFePo4 batteries, right now I feel LiFePo4 lithium batteries are closer to that 2013 flat panel tv than they are to that 2007 model, and they are certainly way beyond that $30,000 36 inch panel I saw at a trade show in 2001. Sure they will continue to improve, but like that 2013 flat panel TV, even now 7 years later it is good enough for daily use. Now I don't know what sort of experience this guru had with LiFePo4, but if it was based on the products that were shipping as little as 2-3 years ago, and how they were being installed, I can see why he might be soured on the technology.
It is not that the batteries from 2-3 years ago from the better manufacturers were all that bad, instead of lot of it was installations being designed by people with no experience in Lithium batteries, as well support hardware such as companies that should know better putting out so called "Lithium" converter/chargers that were little more than brain dead versions of their lead acid chargers with a premium price tag. (this is one area that still needs improvement, but it is starting to get there). On the installation side of things LiFePo4 Lithium batteries prefer the same temperature range that humans do, so when RV designers install them in locations that see temperature extremes like the tongue of a trailer in a metal box in direct sunlight, no one should be surprised when they experience a premature death, but so often instead of admitting this was a design mistake caused by people that thought "drop in" meant direct replacement, these people and companies blame the batteries for their own mistakes.
Ike
p.s. the advice that LiFePo4 is not ready for prime time and to go with AGM is the exact same advice I was giving to most people on this subject in about 2019, a couple of years makes a lot of difference.