I just looked up Square Cash, and it seems like it launched in 2015 according to Wikipedia. Everyone I know (who I would want to send money to/from) was already using Venmo by 2012, 2013 at the latest. I've yet to encounter a single instance where I wanted to switch, nor (anecdotally) have I heard someone voice a single complaint about Venmo in-person.
Venmo got to market with a pretty much pure product before anyone else, and has yet to give any cause for switching.