We don't know if he is though that's the point. I wouldn't say we didn't attempt to replace Lukaku but we did fail too. Remember as well it is Koeman who has insisted on increased productivity and goals all over the pitch, something most of us were into when he sold it. He's failed to deliver on that one thus far.
I can't imagine Walsh had free reign to sign a striker. I think more likely koeman had a very short list for him to work from and Walsh can't force anyone to sign for us
The impression I get rightly or wrongly is that all the cheaper punts are walsh's and all the big money buys are what koeman has asked for. If that's the case no Walsh shouldn't be sacked and koeman clearly has too much power and not enough talent