I don't believe the dozens of 'young' people have never played an RPG before, or an MMO or a MOBA or a RTS. Point being there is no chance any person who has touched a videogame would deride the vanguard. NO CHANCE. Children could give a better explanation about party composition than what was shown here (I get no one choose vanguard but you can still have party structure with mostly backline)
Like I get it's to sympathise with our MC but it's so horribly unrealistic I can't even fathom it.