The article is pretending that having a meeting not only waste half a day but actually waste a full day. Your point B is not reflective of the actual content we are discussing.
The article suggests that makers tend to take on ambitious projects that take large blocks of time to complete. This is objectively true; even today. Most of what is built is ambitious or takes large chunks of time.
Editing some text or repositioning a button or something trivial is 30-min and does not require thought, but most everything is not this. Most everything involves large chunks of time and interrupting this chunk is certainly a disaster.
A) “All meetings are a waste of time.”
B) “There are productivity tradeoffs between a managers schedule and makers schedule.”