I’m not sure why anyone would suppose that an entry level product needs the same profit margin – long term or short term – as a premium product. That’s almost never the case.
In this situation, just because the cost of making the PS5 fat is less that $50 more than the PS5 thin, I think there’s very little chance that the consumer will only see a $50 price difference.
Finally, I suspect that the adopters in the first 6 months will prefer the premium versions of both consoles. The production will likely reflect that. It reminds me of a board game kickstarter where the campaign is designed around most buyers opting for a deluxe option. If more than 20% of your customers are opting for the entry level of a kickstarter game, you probably effed up the pricing tiers.
So even if the PS5 thin costs more to make than it sells for, it may not be a big deal for Sony.