You don’t need to necessarily have 5s. Anecdotal evidence says that cover maxed 4s are actually your best bet since their powers scale wonderfully. If you have cover maxed 3*s those will work too, although health will need to be looked at. Try taking characters who can burst heal the entire team like KK.
I like Balance of Power since it allows me to take all of my cover maxed 4*s who aren’t leveled out for a spin. Definitely a slow event to rise in but its a nice training mode event for testing out new combos.
I’m thinking he means Clearance level 5 for the event. Not shield rank.
Nitefox - the event rank doesn’t set who you play matches against. It sets the rewards. Also, in this event 5* are not good to use their health is actually lower than 4*s.