The same exact argument could be made that Lockhart impacts XSX sales, which it most likely would.
Lockhart can exist because you price Series X at a premium to capture margin and have the powerful box. Lockhart will be a strong driver of sales into your ecosystem.
More likely than not, Lockhart buyers would not be Series X buyers until a price drop. Those focused on the tech will go high end, everyone else is more price sensitive. Only having a box at $499 is a tough sell when your competition can match you there and undercut into the ecosystem by pricing 40% lower.
Remember the biggest jumps this gen are CPU and SSD. Lockhart will have both. The window dressing with graphics will not be the biggest change this gen.
Even before the github leak, I had been hearing rumors of and seeing the value in a 9-10 TF box for PS. They possibly hit their sweet spot on price at $399 and can work between the MS boxes.
A $499 monster versus a fully back compat $299 box with game pass is a tough sell.