Robot Framework allows Keyword Driven Testing and even behavior driven one. Protractor is library not a framework, with inclusion of jasmine we can create Behavior driven development with protractor.
Robot can be used for REST and SOAP service tests, database tests. Protractor alone cannot perform API testing but with help of Node packages we can achieve it.
Protractor has inbuilt capabilities to run our code in parallel, Robot depends on the Pabot.
You cannot write complex application in robot framework, writing if..else is not possible, only you can use if block.
Writing nested loop in Robot class is not possible but protractor can do it, still it is difficult to break the loops in protractor.
Finding a experience person in Robot framework is difficult, not that much difficult with protractor
Robot Framework can test things other than just websites, like FTP, MongoDB, Android, Appium and more but Protractor can be used for testing web applications