Failed a mission with no way to prevent it

I just tried to do the lvl58 "deliver the bomb" four player mission in Canny Valley to try and get that legendary sniper rifle, it was actually going perfectly we had a virtually impregnable fortress and got the bomb to the launcher pretty easy, had all boosts on and even had everyone mowing down enemies with ease

so far so good…except in the last minute they pulled out the trap immune, tank, bullet proof, melee proof mini boss that summoned volcanos…. killed the objective in about 3 hits

now ive been with this game since it was playable on Xbox, before the term "battle royale" was used in gaming, and ive put up with a lot, like A LOT of crap, but this is where i draw the line, its effectively telling the player to shove up their rear end, and give up, there is no snowy chance in hell anyone can complete a mission if the enemy in question is nigh indestructible, unstoppable, and so armed to the teeth with buffs it gives Doomsday a run for its money

I dont see the point in having these ungodly hard mission if people who are over leveled have no chance at winning, strategically I cant see anyway to win this without someone else breaking the game to win I mean it was so bad that me a base lvl 62 player and 3 base lvl 100+ players could not do anything to stop it from happening, now I dont normally do 4 player missions, but is this super common with mini-bosses? because I dont see how these missions would even be possible with Dollar store Doomsday running around