Hi!
No, it is not contradictory.
The WS-I Basic Profile aims to clarify things in the related specifications that are unclear and advise against things that have proven to cause interoperability problems etc.
So, while the schema allows for additional elements after the SOAP <Body> element, the BP forbids it.
Perhaps there is some case in which you would want to use additional element(s) after the SOAP <Body>, which can be done as you note. However if you want your service to be interoperable with, for instance, clients developed by others and/or on other platforms,
you should avoid this.
Best wishes!