You can work around it if you want...
Now, I'm not really sure what would make the Enterprise tick here, but I can't help wondering if the conclusion isn't a bit silly. Sure; when you look at the phone "as is" then he's right; on the phone the data being held by the apps is sandboxed.
But what's the problem? If you're using external storage such as SkyDrive or a SharePoint environment then there's nothing stopping applications to put their data on the same place. I'd say its a win-win situation here; data can be shared but only in a more restrictive manner. Because the primary data (which is apparently very important) sits on an external storage there is also no risk of said data suddenly becoming lost should the phone for some reason suddenly get out of the picture (stolen, lost, breaks down, etc.).
Granted; its not very redundant because commonly speaking the phone would always hold 2 locally stored copies (depending on how said data is being used of course). But then again...
OTOH; I also see a possible advantage. Its also possible to setup the phone so that it only accesses online data on a temporary basis: it copies the data to a temporary location, data can be edited and afterwards data is sent back to the online location and removed locally.
I fully see that this scenario probably won't benefit everyone and I fully agree that you're working around certain aspects of the phone. But really; doesn't this also /enhance/ security? As soon as said phone is reported lost you simply lock down access to these files thus resulting in a possible attacker being unable to access said data any longer.
So how is all that extra security bad for the enterprise?
Speaking of privacy... I'm surprised no one mentioned that all options which could affect your privacy are fully opt-in. From MS wanting to get data for research right to MS asking to get access to your browsing history, speech commands or picture searches. If you don't say "yes" then MS won't "snoop" on you.
Heck; they don't even bother asking about certain options; you just have to find them yourself in the settings. IMO that would also be an important qualification for a mass-used phone, especially since one of the competitors is fully opt-out where privacy is concerned.