I do not understand who you interpret "compete", from my point of view every actor on the market offering products for a certain group of customers is competing, since the customers have limited resources (time, money) that are needed to consume those products. Since LoL, Dota II, HotS, maybe also Smite and in further development states also Supernova can be all counted towards the MOBA genre, they are competing for customers.
Since Supernova is no AAA-title like HotS that enjoyed massive marketing and great public interest just because of the fact it is a game developed by Blizzard Entertainment, it probably will not have such an impact like HotS and also will not have as much players as HotS, LoL or Dota II have, but the game will compete with other MOBAs. If not, Bandai Namco would have done or will be doing something completely wrong.
They are the publishers and they will, maybe during the open beta or at least at the official release, do what have to be done (marketing) to build up a player base Bandai Namco and Primal Game Studio can subsist on.
Sorry for grammar mistakes, I am not used to explain economy in English.