Sure you can protect against this - there are several companies that use machine learning to spot small differences between selenium and real users (mouse delays etc).

For example, it might detect that a mouse click is dispatched at exact intervals (and block it). To which you'd think "I'll just add Math.random() * 2000" which it'll easily detect as well.

It's _definitely_ doable, but it's not as trivial as recording a selenium macro. (Not to mention these tools look for selenium presence and extensions anyway).