I agree that PF1 is less streaming-friendly than 5e (plus it does not have D&D's name recognition), so CR using PF1 would have been less succesful (while making PF1 slightly more successful). 5e has really benefited from the rise of "watching other people play games on the internet" as a thing; CR is obviously a large part of that in our timeline, but but how much its absence would have hurt 5e is hard to say. Other streams would have picked up the slack, but how much?
I strongly disagree the 4e is less streaming-friendly than 5e; at its core it is simpler and more consistant. Assuming that dates posted upthread are accurate, it was obviously too late to save 4e, so 4e CR would have had an impact similar to PF1 CR (albeit to a slightly greater extent). Now, if Mat Mercer had got the idea of streaming his earlier 4e campaign, that would be a more interesting timeline to spy on....
EDIT: To the people saying that 5e sold gangbusters before CR launched: Of course it did - it was a new edition of D&D! That it continues to sell that well (better even) is a confluence of many factor, but the rise of streaming of tabletop games that CR exemplifies is definitely one of them.
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glass.