I can't speak for @stellabelle or her post, but in my post I list the advantages which Synereo has over Steem. These are theoretical design advantages, and the main advantages are composability, but also a functional programming base. This allows Synereo to be very adaptable to change, modular, secure, but I'm not so sure if it's going to have better performance than Graphene which is why I did not list that as an advantage. I do think it will scale but I think they made a trade off to have maximum flexibility and security by going with certain choices, but this could cost in terms of performance because it's more generalized computation.

If Graphene is really specialized for performance, but Synereo is designed for flexibility, then it could evolve where Steemit is very fast but then you can't do as much with it, while Synereo is extremely flexible but not quite as fast. Synereo has to be fast enough to be compared to Facebook, it doesn't have to be faster than Steemit. I think that Synereo can achieve 1000 TPS, maybe more, but I know Graphene can theoretically do 1 million TPS.

References

1. http://martinfowler.com/articles/lmax.html
2. https://www.lmax.com/pdf/lmax-exchange-wins-best-trading-execution-technology.pdf