No it is a horrible mechanic.
To A and S classes, we will reach level 400 boss as early as 3-6 hours in the new day. Do you know how tough it is to fight level 400 bosses throughout the other 80% of the day, especially the ether consumption.
Not to mention that for the first 2-3 hours of the day, probably only 5 members get to touch the boss, leaving their BP to waste.
To A and B classes, they don't have fully active members throughout the day. For some who can only make it at night, the boss is already at level 200/300s when they logged in. Making them unable to clear a single boss mission because the boss is already undefeatable then. And they need those rewards to become stronger.
Soloing the boss means that your teammates can't get the reward. No matter which party class, it's a lose-lose situation.
It's an outrageously bad mechanic, and the amount of complaints to remove this is serious. Even more than the usual "increase ___ limit please" requests.