The performance on my iPad Air 2 is horrible since upgrading to iOS 13.3. It wasn't great under iOS 13.2.3, but wasn't terrible. Now I'm seeing apps take a long time to open and sometime crash when trying to launch them.
For example, tapping a YouTube link had the entire app hang for 10 seconds with the audio playing in the background, but no video playing. GMail now tends to crash on launch when tapping notifications and I have to launch it again. I was hoping this would be temporary, but it's nearly 24 hours later and it's not any better. I tried restarting, but that didn't help.
The Air 2 only has 2 GB of RAM, but I don't think things should be that bad. It seems like iOS 13.3 is using more RAM for stuff.
My iPhone 7 Plus seems to be working fine.