In business, no one can hear you scream.
As a large organisation with a mix of PC and Mac desktops Outlook 2011, and God forbid!, Entourage have been dismal failures as Exchange clients compared to Outlook Windows. The tweaks to Outlook 2011 does little to improve this. Forget it.
We also have Outlook 2015 Mac through a O365 sub, and whilst this is an improvement on Outlook 2011, it is still sufficiently far from Outlook Windows that its utility is second class. I am hoping that MS will address the shortcomings of Outlook 2015 before formal release and so make it 100% feature comparable with Outlook Windows, but I won't hold my breath.
You might ask why we use MS products in general, Exchange in particular and O365 subs? In short, because they are generally good products that require fairly minimal attention once set up and there is a large pool of people who can support them when they go wrong. For a business, renting software can make more sense.