I also noticed this and used the BJ strat on the boss, I took me some time to understand the mechanics as while some of the information is good to read it leads to aspects of the game not really being intuitive. Was able to beat the game once I understood but I will say the BJ strat is way to op and with the boss it feels needed. Also heath from the upgrade character seems too low, only 30% I found to not be enough if I was trying to kill as many enemies as I could.