I don't think that's fair. Pretty much all the issues people complain about with third-party keyboards occur with ALL third-party keyboards. They also occur almost exclusively in Apple apps. If you read the Swiftkey forums, the developers have been pretty clear that these issues are Apple bugs that they have reported, and there are simply no workarounds available.
How is it not fair to put some blame on both parties? I am not saying that Apple is perfect, they do need to fix a lot of things in iOS 8, but devs are also partly responsible for some bugs. Not all bugs are the result of iOS just like not all bugs are the result of dev issues.