Given that the vast majority of users don't have wi-fi problems, I don't see you successfully arguing that the iPad is not fit for purpose.
I had an occasional dropout when using my home router, until Apple updated IOS, and now it's fine. I didn't have any problems with any other wi-fi access points though, so I am prepared to accept that the cause was the result of an unforeseen interaction between the iPad and my router. To be fair, it's impossible to test against every case, there are a lot of different chipsets and designs out there.
I think you need to ask yourself if you want the iPad. If you do, buy a cheap but modern access point and hook it into your Sky router. If not, then try getting a refund, but accept that you may need to pay a restocking fee.
I know it's not ideal, but I think it's the best outcome you can expect.