Thanks for all the replies.
It does indeed turn out my copy was faulty. I got the replacement today and everything is fine
Very sharp at f2.8 just as I hoped it would be.
I was worried that because I had only used the primes up to now, IE the magical 90mm f2 and the equally amazing 16mm 1.4
The zoom wouldn't be up to the same standard that has drawn me the Fuji system, but thankfully things are looking very good.