I think reactions can absolutely be done away with, if only one reaction option is available, such as ❤️ or 🤙. A zap already tells me that you "like" the post, and even tells me how much you like it, based on how you zapped.

However, if there are a wide range of reactions available in the client, then reactions can still have value and provide additional context. They can tell me you found the post to be humorous 🤣, surprising or mind-blowing 😮 🤯, or that you found it to be an astute observation 💯 🎯. This is all context that the zap alone does not necessarily provide.

There is also no way to give a negative reaction as a zap, such as 🤮, 😡, 😭, or 🙄. There's an argument to be made that taking out negative reactions is a feature, not a bug, but I think we also lose quite a bit by not having the wide range of positive reactions, too.