Thats hardly scientific. Have a source to back up those claims?
I've never heard of kratom alkaloids having a saturation point, yes theres opioid receptor agonist/antagonists in kratom that balance out the high, and in some ways put a ceiling on how hard you can hit your receptors, but saying you can't absorb above a certain amount doesn't make any sense, and theres no proof thats the case. I think of it like how CBD in cannabis modulates how THC anonizes the cannabinoid receptors. Or how naxalone is used in opiate overdose.
Extracts aren't just for people who want to get super high on kratom, they don't have all the tannins and crap whole leaf has, that for me personally tear up my digestive system in a manner of speaking.
And alot of the bad rap extracts get are because alot of them are crap. There are really good extracts out there, but alot of expensive weak stuff as well. I use extracts almost exclusively, and would take them over whole leaf any day, and to be honest its not that much more expensive.