An increase in ISO of one stop on current digital cameras is undetectable. Same benefit as f/2.8 vs. f/4.
The "faster lenses are sharper" claim is rarely true with current lenses as well. These mirrorless lenses are astoundingly sharp in most cases.
Personally, I think large maximum aperture lenses are mostly a waste of money in the digital era. For example, in the Nikkor Z line, I can spend $2,400 on a 24-70mm f/2.8 S and have an enormous, heavy, extremely expensive lens that's rather limited. Or, I can get a 24-120mm f/4 S (both are...
I'm surprised it shows a TBA number. It was my understanding that Amazon drivers aren't equipped to handle signature requirements. I buy a LOT from Amazon, including items around $1,000, and they are just dropped off by Amazon. This includes a Nikon Z5 and some lenses in the $1K range. But...