Why are APK'S buggier than Play store downloaded apps? I had downloaded an early copy of some game, as its apk was put on apitoide after the app was available for 15 mins. Its an app that allows you to fling spheres at imaginary monsters. 

Anyway (Ha-Ha!) The apk was a horrible, buggy mess, whilst the play store version was significantly cleaner.

** Is there any reason to why APK's are more 'broken' than their play-store versions? **
The Play Store version is the official version, which often has updates pushed out on a regular basis. Developers put effort into maintaining the play store version. If you are using an APK version downloaded from elsewhere, there is both the danger that you have put malware on your device and the high probability that it's older than the official release.