no no no, you now have the suspension of an AWD sedan.
Remember, if you're going up 2.5 inches then the down must be sacrificing 2.5 inches. It's numbers and math and geometry. If there was only 4 inches of down-travel, then the math says it's now only 1.5 inches of down travel. LOL
I was driving my Westcott-pre-load-collar-equipped truck offroad this past weekend and I can assure you that the wheels move downward by more than 1.5 inches.
The long & short of it (pun intended) is that yes, it is certainly true that a pre-load collar is a bit of a sacrifice. This is my 6th offroad truck over the past 35 years and the first one I've put a pre-load collar lift on. The main reason I did the pre-load is because it was available for these brand new trucks, second is because it' relatively inexpensive, and third is because the sacrifice is minimal for the truck.
All the theoretical keyboard punching math & geometry and why this (pre-load) is such a bad idea doesn't change the fact that this is not a rock crawling truck. People who try to make it into one will inevitably spend a shit-ton of money and, at some point, admit to themselves that they bought the wrong truck.
For what it is, the GX550 is a really nice offroad truck (based on it's width, length, weight, offroad angles, suspension design, drivetrain, price, etc.). A little tweaking here & there can make some small improvements with acceptable sacrifice. Gaining clearance for 35" tires while sacrificing an inch or so of drop is acceptable in my opinion. If I want to start Baja racing this thing, or try King of the Hammers, then I'll drop $10k into an entirely new suspension. But first I'll probably admit that I bought the wrong truck.