Isn’t this the difference between building monolithic platforms versus small pieces of functionality like microservices or open source gems/modules?
The relationship between complexity and strategy seems to be that the company’s strategies dictated their approaches in implementation complexity. Rather than complexity tradeoffs were discussed and then a decision was made to update the strategy.
As an aside, this piece brought me back to my time at Microsoft. I was in the MSN/Windows Live group for a while and one story that is particularly similar to the one you tell about OneNote is for MSN Messenger and Xbox. Rather than waiting a long time for MSN Messenger to support Xbox for their game chat, they decided to roll their own.