Has some scholar made a study of how often Horatio says yes to Hamlet? He affirms him in so many ways, so many times. It is his essential role in this play – to just affirm and keep Hamlet from just talking to himself all the time.
Horatio is so much Hamlet’s reflection – it might be possible to do a production wherein Horatio is just Hamlet’s alter-ego – another side of himself that just listens to him. The only scenes that would be trouble for are the two scenes that Horatio is in without Hamlet – the opening and the one where he receives the letters. Every other time, he could just as easily be in Hamlet’s imagination.