Serenity Caldwell, writing for iMore:
Despite receiving several updates in the last few months, Google's apps haven't been updated for Apple's larger tablet. And there's no hope, as there is with Facebook, of using Google's in-theory-HTML5-and-therefore-iPad-compliant website: Google's standard web view on an iPad flat-out punts you to the apps—if the website even correctly detects you have the app installed. I can't count the number of times I've seen the websites try and send me to the App Store to open a spreadsheet, when I clearly have Sheets already available.
Trying to request the desktop version of the website won't work, either: You won't be able to scroll, or tap on anything that requires a double-click, and any link you do manage to make work will send you right back to the mobile environment.
Compare Google's subpar iPad Pro "work" to Microsoft, which was quickly ready for the iPad Pro, iOS 9 multitasking, and Apple Pencil. I've switched to Office 365 for my personal spreadsheets and Word documents, and, if the situation doesn't improve, I'll consider other solutions for collaborative docs as well.