They do not share the same SoC.Depends. Since all iPhone models use the same SoC, the A17 could bs part of the delay. I don’t mind if the Pro‘s get a later release date (they have done it before).
Apple started that type of differentiation between Pro and regular iPhones last year and will continue to do so (as it increases the margin for the regular series).
Besides: I don’t think they will delay iOS 17 because of delayed iPhones. The 12 series was delayed until October (presentation was on October 23rd 2020). However the corresponding iOS 14 came out in September as usual (on September 16th 2020).