So Lockhart is rumored to be $300. Meanwhile both Series X and PS5 are rumored to be $500. Sony has no $300 SKU at all. If these rumors turn out to be true then Lockhart is $200 less than the other two systems. At such a price difference, should it be counted as part of Series X sales, or should it be counted separately? 

Let me put it this way. Let's suppose PS5 sells 120 million units lifetime, and Series X sells 30 million units lifetime, with Lockhart selling another 30 million units. This brings the total gen 9 sales up to 180 million units lifetime. Should this hypothetical scenario be seen as Sony having gained ground against MS or lost ground? 

Clearly 120,000,000 sales is a dud.

I changed my other question a bit to make it clearer. Thanks. 

Doesn't PS5 already have a lower priced sku of it's own? Rather ironic you're speculating about things based on rumours of prices and an unannounced system, yet conveniently overlook something that's already confirmed.

Lockhart, whatever it is will still share the same architecture as the Series X, and still be considered a next-gen system. No different to Xbox One X or PS4 Pro from this gen in that respect.

Revenue made on console sale prices matters very little (see: Nintendo profit margins). What matters most is getting your system in people's homes. So yes, Xbox gaining more market share would be worse for Sony and good for Microsoft.

What is the PS5 lower priced SKU? Are you talking about the diskless PS5? That might be $50 to $100 less than the disc version, and it would still have the same specs as the main PS5. So I don't quite see that as a different system. 

Why would it be counted differently? It shares the same library Series X, they're one platform. 

It's just a weaker Series X and it seems to be fundamentally the same platform. So the sales ought to be lumped together.
Changing, companies, let's say Nintendo had 2 SKUs at launch for the Switch's successor. One was right around Xbox One performance, or slightly weaker. And then one was super powerful for a hybrid with roughly PS4 Pro specs. They would still be fundamentally the same platform. Both would be replacements for the Switch and have an identical (or 95% identical) library.

So why do specs suddenly matter now?

Both your title and OP completely phrased the issue around pricing, stating 'Sony doesn't have a $300 sku', and conveniently ignoring their digital-only system that's already been confirmed, and likely to be $100 cheaper.

So is the magic number $200 less than your competitor? Is that when it becomes unfair, or not equivalent anymore?

As far as we know, Series S or 'Lockhart' will play all the same games as Series X, with the exact same architecture. So outside of some performance sacrifices, it's the same system.

Regardless if it meets your requirements, as long as it helps sell more Xbox systems it'll be a gain for Microsoft.

Ofc it should

It never even crossed my mind that someone might somehow consider the diskless PS5 to be comparable to the Lockhart. It's like someone telling me they drive a four wheeled vehicle, and then pulling up with a motorcycle and a sidecar. Technically four wheels, but not what I had in my head. Had I anticipated such a weird response, I definitely would have phrased things differently.