Good question.

A web chess game is turn based with some basic logic to sync the clock. There are no secrets or complex state like many video games. Seems rather straightforward.

The hard part is scaling up everything around it:

- Stockfish real-time predictions

- anti-cheat monitoring

- the moderation tasks any social website needs

Replace chess with checkers and I think they'd still have ~90% of the same problems. This seems to be more about massive table/data growth than inherent complexity of the core business.

A complete chess game should be a very limited amount of data. I am finding conflicting reports that a typical chess game is 40 to 70 moves.

That being said, if any service suddenly saw a doubling of users within a month, plenty of sub-optimal architecture decisions can suddenly fall on their face which were otherwise adequate at the previous scale.

PVP probably yes. PvE? Not really. The algorithms for a competent engine are fairly CPU heavy.