I felt a sort of haughtiness in the letter, like "you don't understand what chat is, but we do, and if you look at our success, you will never understand what chat is, but we will." This was not a letter of advice, but instead a letter of intimidation.
But if I give them the benefit of doubt, maybe it was just an ad. Nothing more. Nothing less. One that touted the underlying coolness of Slack and the platonic posture of Microsoft.
In all of this, Slack misses the point of Office 365 chat, e.g. tie users together when working on Office products, and build collaboration features for Office users. Maybe Slack slacked off on what the market was requiring now and was not able to keep itself up to date with what companies like Microsoft needed.
For reference, here is the ad: http://www.historyvshollywood.com/reelfaces/jobs-apple-welco...
There is an interesting welcome ad that Data General made when IBM announced their entry into the minicomputer market in 1976, although Data General never actually ran their add. It said:
They Say IBM’s Entry Into Minicomputers Will
Legitimize The Market.
The Bastards Say, Welcome.