4 12V 200AH deep cycle lead acid batteries cost $1552 on Amazon and hold as much energy in practice as a 100AH 48V LFP battery which last 15 years, minimum, and only costs about 6% more up front. (Not linking to specific batteries in order to not shill for them, but do a little searching for 100AH 48V 4U server rack LFP batteries on youtube, and you will find dozens of tutorials.) Quality inverters last 30 years, not 10.
Are these people TRYING to light money on fire? Are they fronting for someone by trying to make solar look impractical? Or are they just stupid?
If you want something better and brand name, you'll pay more. Sometimes, significantly more.
It still doesn't make sense to use lead acid for off grid, deep cycle or not. UPS systems still use them because lead acid loves to stay charged at 100% and not drop below half, which is fine for UPS that are intended to run only during occasional power failures.
LFP batteries also last for thousands of cycles and are safe, probably safer than lead acid.