Microsoft is rapidly moving away from this type of situation. You buy 365, always have the latest version, have nothing on prem to maintain, can beta test everything in the cloud before general release, AND most importantly, youre not getting an empty infrastructure/platform that isnt useful out of the box.
Sharepoint by definition required an architect or someone to flesh it out. Microsoft is taking on that role of turning a skeleton into a body.
Their pricing is more like (a made up example): Exchange $2, Sharepoint $2, Skype $2, OR Everything + BI, Teams, Groups, Planner, Flow, PowerApps and whatever else they make/dreamup this week for $3. It makes no sense to buy 2 things from Microsoft over the bundle. The pricing is even more apparent when you look at their mobile management offerings, and its cheaper to buy 4 products than it is to buy 2. So now that you are "getting Teams and Planner for free" you might as well try using them before shelling out for Slack and Trello. Plus compliance worries are handled.
Also, it's fairly easy to "leave exchange and sharepoint document libraries" if your setup and permissions arent complicated. Microsoft is pulling an Apple, and abstracting the filesystem away so you use Planner directly to store planning data, in a proprietary, non exportable format, instead of having a storage locker to store files. These "freebies" exist to make it more painful to leave the ecosystem once you have them up and working. That said i am guessing most companies dont have a ton of buyin to things like Planner or PowerBI yet.