I just went through this exact decision tree. 2015 LX570 or new/near new LC 200. I just can't get past the front end of the 2016+ Lexus.
Lx570 - I'm not sure if the dealers are selling these yet due to the passenger seat belt/airbag recall. When I was looking, there was a 37k mile 2015 Grey LX570 at my local Lexus dealer but they were not able to sell it as a CPO, or even as a non-CPO discounted until the fix came in. Some vehicles are fixable now, others are not yet. The dealer wanted $58k for it anyway, which I felt was too high. It was the lowest mileage, cleanest 2015 LX570 I had seen, or have since seen. I would not worry about the AHC. It is a hydraulic system, not air, and is very robust unlike the Land Rover or Mercedes systems that have deservedly bad reputations. I had a 2000 LX470 with the original AHC system still functioning fine at 285k miles, just with simple flushes at 60k mile intervals. The 570 system is even more robust by report.
2018 LC - Do not buy a remnant 2018 at $78k. Eric Sarjeant (member on here) will sell you a new 2019 from Ed Martin Toyota in Indiana at invoice, which is $78k, with your choice of color/interior. The 2020s are about to come out, and he sells at invoice which probably won't be more than $1-2k increase from this year with no model year changes. Fly and drive
"every option" likely means it has the DVD screens on the back of the front seats, which to most on the forum is a negative...was to me. One of the benefits of 2018+ is NOT having those screens like all of the 2016-17 did. They leave a big ugly hole when you remove them.
I would negotiate the remnant 2018 down to the cost of the 5k mile one, $73k. Others have gotten them down to around $70k. It is 2 model years old as of August. I would pay the $5k extra for a current model year.
I ended up finding a 2018 in North Carolina for $65k. 34k miles but pristine condition. I saved $13k over new, which meant I am allowing myself $13k in mods in exchange for the used truck. But, there are times when I question that decision. 34k miles is 3 years of mileage for me. But, well maintained mileage is not a huge issue on these trucks. Anyway, getting beyond a 5 figure savings was the tipping point for me, and I will do mods to the truck. If it was only $5k difference, I absolutely would have bought the new 2019 from Eric.