I avoid iTunes as much as I can on my mac as well, it's horrible. In terms of performance I think the App Store they ship is even worse, it's a travesty of an application and I couldn't understand how Apple would ship something so unpolished and... non-native feeling. I might be wrong but it feels like it's web wrapped in a native shell and it's performing horribly compared to Electron apps.

EDIT: To be fair most of the slowness could be perhaps be attributed to slow network requests as well.