Ot doesn't sound like thd OP has a complaint yet; right now it's more of a concern. The fear is that without a strong leader ability to tie the team together, (i.e. Mandalorisn leader) it won't be possible to beat the top tier and get all the rewards. Could that be true? Absolutely. Do we know for sure? No.
Given that none of us have played in the event, nobody really has anything more they can say other than, "I understand your concern and that concern does/does not bother me."
For all we know, the win condition or battlefield bonuses may make a Mandalorian squad viable even without a leader. On the flip side, it could make it impossible to beat without a Mandalorian-centered leader ability.
I honestly think there isn't enough information for there to be an argument about this.