Competitive coding, despite superficially involving typing code into an editor, has almost nothing to do with working on large pieces of software. It's a lot of rote memorisation, learning algorithms, matching them onto very particular problems, and so on, it's more of a sport. Just like playing too much bullet chess can be bad for your classical chess I can honestly see how it gets into the way of collaborative work.
From where people assert so confidently such nonsense? Chess is 90% tactics at the under 1800 Elo level or so. At the 2700+ level? No way.