The message you're seeing is telling you that some features supported in the version of the app that recorded the script are not supported by the version of the app playing it back. The message is not telling you that the script actually contains any of those features (hence you'll see it when you play back even a simple script that just applies paint).
This is because the only way to find out if any features in the recorded script are not actually supported would be to scan the whole thing, which would take too long. So, in the majority of cases you will find that the script should be reproduced with no problems. It's certainly not the case that 'most' of the features are not supported by Studio.
The Palette Knife has a couple features in the iPad version but not Studio. Specifically, Studio doesn't support two of the modes - Blur and Wet Blender. Other modes of the knife should work fine. The post you found on the forums probably indicates this. It shouldn't be saying that the palette knife doesn't work, because that's not the case.
If you used the standard palette knife modes (edge and flat, or smear) when mixing your imported photo it should be reproduced correctly when playing with Studio. If that is not the case, we can take a look at the script and see if there is anything wrong in there.