You can from Xbox still connect to both Nintendo PC and mobile the fault is at sony´s there is no denying it.
Maybe I misinterpreted it, but I thought in the context of your previous text that actions were done one after other.
(1-Create your account on PC
2-Connect to your Xbox/Switch
3-Connect to your PS4
4-Can't reconnect to your Xbox/Switch because of your previous connection to PS4)
That's why I made the precision in my first sentance. In this case, the step 3 is impossible.
You're confusing between Sony's position on the Crossplay (attackable in its posture, but maybe you do not know all the ins and outs behind this case, are you a little bit aware of the Microsoft Crossplay terms before you make your opinion?) and not to warn about the consequences of an account assignment for which only EG is responsible.