I hope that you are wrong. My XSMax is running perfectly fine with 17.4 and I would love to keep on using it with full iOS support until the iPhone 16s get released.My XS is less than 6 months old (courtesy of Apple) but I speculate that iOS 18 will not support it.
If it does get dropped, as you speculate, at least it will keep getting security updates until the new model arrives.