The author worked on the team for 8 years, including the transition to Roslyn which unified much of the expensive concerns around VB.NET and C#. It's the author

The author worked on the team for 8 years, including the transition to Roslyn which unified much of the expensive concerns around VB.NET and C#. It's the author's extremely strong familiarity with that engineering system that led to their claim. In the post he walks through how team sizes grew significantly smaller across the board. 15-20 people would be far larger than the current C# language/compiler team.