Welcome to the "little brother" LC! My wife and I also had our own 100 series, both had the factory rear e-locker also, which was available in the early years.
You mention that the GX is not that much smaller, but when we purchased ours, I immediately noticed (being a large six footer, that the 100 series was much wider, which was noted with the fold-down armrests next to the center console in the 100 series, but NOT in the GX. On the GX there isn't room to add fold down armrests next to the center console, the center console IS the armrest! Also, I've noticed it's not quite as deep behind the seats. I was able to sleep fully stretched out in my LC with middle seats folded down, but for the GX I need to slide the passenger seat forward and back fill the space between the front seat back and the folded down second seat to completely stretch out for sleeping. With the 100 series third row seats folded up, there is far more room in the GX with the third row seats folded down. Although if you remove the third row seats in the 100 series, you do get back a lot of space!
Even though the GX is a wee bit smaller, the advantage is we definitely like it WAY better on tight trails when off roading! This being on account of it having the same foot print as the 5th Gen 4R, which of course is one of the most trail worthy vehicles available.
And regarding the diff drop, correct, to fit 35" tires on my LC I had to do the 3" suspension lift, diff drop and make my own 1.75" body lift. With my GX, I did a 3" suspension lift, 34" BFG M/T's, BMT (body mount trim, common for the 5th Gen 4R's and GX's) and a wee bit of trimming of the inner wheel well and called it done. I asked questions about it and everyone says it's not necessary. 3 years into my build and never had an issue!