Gmail.app for iOS is incredibly sluggish (on my 5S) while Android's version on my Moto G is pretty snappy, so you're not experiencing the same thing at all.
I run both Mail.app and Gmail.app on my iPhone because I'll often get the push notification for Gmail.app, tap the notification to open the email, get frustrated and tired waiting for it to load and just go manually refresh Mail.app and see it almost instantly.
I run both Mail.app and Gmail.app on my iPhone because I'll often get the push notification for Gmail.app, tap the notification to open the email, get frustrated and tired waiting for it to load and just go manually refresh Mail.app and see it almost instantly.