My iPad Air 1 (32GB wifi-only running iOS 11.4.1) posts about half the speed of what my MacBook Pro mid 2012 posts. I am traveling at the moment and staying in an Air B&B home in Boise ID with CableOne internet. I happened to test the speed about an hour before I saw your post.
The MBP wirelessly shows very close to the 100MBps speed that is CableOne's standard. The iPad Air is reporting 48mBps, both with Ookla. That may change with proximity to your wireless access point.
To make sure local signal interference isn't playing a role, please see this Apple article:
Potential sources of Wi-Fi and Bluetooth interference - Apple Support