Currently I've noticed that some big pages take a long time to perform ajax refreshes, I feel this is because of the dependency of the server to handle everything.
With ReactJS the client handles the drawing instead of the server having to push all changes to the client, the client reacts and handles the changes. React also uses a feature to only apply the changes, so you don't have to reload your entire DOM.
Creating a simular page in plain html,javascript and php on a simular server currently makes such a big difference in performance.
If Outsystems were to solve this performance lack, I'm sure it will become so much more popular (because there will only be upsides in using the platform)