Rather than being a direct downgrade, I believe it would be a small incremental upgrade, like Apple used to go from vanilla model to 'S' model every succeeding year in the eras gone by. So, if this piece of news is true, which of course requires consuming a grain of salt alongside, then we are in for an iPhone 18 which would be approximately equal to an iPhone 17S, rather than it being an iPhone 18, in purpose, in vein and in totality.
The Apple iPhone 18 is not due to be launched until next year, several months after the iPhone 18 Pro. According to the latest rumors, Apple's iPhone base model will not only launch later than usual, but will also receive downgrades to reduce production costs.