"Anyone think differently?"
Nope, I agree.
When someone buys a cheap case back gasket assortment on eBay etc there is no telling what the gaskets are made out of. Most supply houses carry good quality gaskets (hopefully).
Some gasket info...
Screw down backs:
Case back gaskets are sized by their inside diameter and thickness, both O ring and flat types. The ID can be obtained from the gasket seat in the case or the lip/groove on the case back but the thickness is sometimes hit or miss. Measuring a used gasket will not always give an accurate measurement because the old gasket may be compressed to an out of round shape.
You want the gasket to compress fully so that when the back is screwed down the case back seats against the case without squeezing the gasket too much or not sufficiently compressing the gasket...this is where hit or miss and developing a 'feel' for the process comes in. You do not want the gasket showing from the outside after the case back has been tightened (because the gasket is too thick) but there may be a few exceptions to this. You also do not want the case back bottoming out before the gasket is compressed and this is sometimes hard to determine.
When the watch is a replica, vintage, obscure brand, no published specs etc, it takes precise measurement or hit or miss until you determine the correct size. Always lubricate the gasket with silicone or something similar and be careful not to allow lubricant to get down into the case or on the movement. Rolex and some other companies use gasket/thread grease (Fomblin, Krytox etc, aka 'high vacuum grease') and it also prevents stainless and titanium threads from galling or seizing. The catch: Fomblin is about $80 for 20 grams.
I had a rolex 160xx with the case back seized and when I finally got it apart (penetrating oil/Bergeon 5700 case tool and a LOT of downward pressure), it removed some of the threads on the case back (the back was stuck when I bought it). A drop of Fomblin etc would have prevented it.
From the Edwards website:
Fomblin® Grease:
This grease is an excellent lubricant for sliding elastomer seals, and exhibits the chemical inertness typical of the Fomblin® range.
It has a very low vapor pressure and is suitable for use in the presence of gaseous and liquid oxygen under severe conditions.
(Edwards specializes in vacuum devices etc)
Krytox GPL 205 is a little bit cheaper, it's what I use.
Snap on backs:
The same rules apply but it is sometimes harder to tell if a flat gasket is too thin or not. Silicone is fine, no $80 Fomblin needed.
'Red' plastic (polyurethane) gaskets like used on some snap back omega, Gucci etc. No lubricant is used. Gaskets must be an exact fit, sometimes a hassle, easily damaged.