Consider that the iPhone X was on the market for only 10 months (instead of 12) as a result of the delayed launch. Was that in Apple's best interests? Putting the product in people's hands and social circles generates more hype than a virtual product. Look at the Model 3 launch and potential customers who asked for deposits back as time went on.
I don't really see why it matters that the X was on sale for 10 months rather than 12. Did it result in fewer iphone sales in total? I'm sure that anyone who intended to buy an iphone between Sept 2017 and Sept 2018 still did. Those who wanted the X probably didn't lose interest because of having to wait an extra 6 weeks.