You've thrown in multiple un-related things here. Let me try to address them.
- Who's trying to say the 2TB SX doesn't exist? Most, if not all, 'Xbox fanboys' on GAF have also said that it's a pointless thing and too expensive. It's only brought up when used as a "gotcha" to counter any criticism of the PS5 Pro's price.
- I don't know why the 5~10% total sales thing is relevant here.
PS5 Pro's price has set the precedent for all standard future console releases and also the precedent that things like disk drive can be sold separately for even more.
- The 2TB LE SX is not the standard SKU, there are cheaper alternatives of that console. The PS5 Pro is the
*only* SKU, there are no other versions of that console available, and the standard SKU is not even feature complete, thus requiring additional purchases to match the standard PS5 at launch.
I'll use a familiar example to illustrate so it's easier for you to understand.
The Concord Limited Edition Dual Sense is $84.99, which is $10 to $15 more expensive than the standard Dualsense. Is that the only Dualsense someone can buy? No. It just as a higher price tag for the exact same thing because of its status as a Limited Edition thing and most people, who are not specifically hunting for that LE thing, will opt to get the cheaper standard SKU instead. Now use the same logic above.
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Besides, it's more sensible to compare PS5 Pro to a standard PS5 at launch anyway. No one compared the PS4 Pro to an Xbox One VCR, why now.