When they announced they were going to use the SD on all models a year or so ago, they mentioned they were doing so to take time and develop the Exynos and come out with a new chip in a year or so that would rival or beat the SD.
They had to. They were constantly being embarrassed with their own chips underperforming. The reason of course because... cost. Save money not using Qualcomm and keeping things in house. Apple does it. Googled has followed. It's embarrassing if Samsung can't.
And I can see them "trying" to go all-in with the Exynos when it comes out.
You don't put your own flagship against itself by having two different processors going forward. Because if their is the slightest of performance diff... 1 point on a benchmark, people will never accept it and make a stink. If you don't put the SD in the phone, no one will know if the SD would have actually done better on the phone if they can make it run as well as the S23U.