Earlier quoted context omitted.
It's recent that it's the "same" Office though, no? It used to have different codebase (with, I'm sure, some reused code) and even had different release versions (ie: Office 2011 on Mac VS Office 2010/2013 on Windows) I dug a bit and I found this article[1] that says it's now using a common codebase for Office 2016 since January last year, so I guess it's not something new with this new release of Office 365 on mac.…
The quality on Mac is nowhere near the quality of Office on Windows. At least Excel. Slow, crashes, tons of missing shortcuts, etc.
But Excel is the lingua franca of business, so I keep on using it.