No.

The worst 4 Party group in the game is 4 BBs.

Why?

Well, look at 4 BMs.
They dominate the early game with magic, from Garland to the Eye (If you skip Kary until later, which you'll pretty much have to do). The water level is a breeze. Tiamat is weak against BANE and BRAK.
The only hard part about 4 BMs is that usually you'll want to level into the 30s so you will have plenty of nukes for the ToF (revisited).
And THAT is only hard because you'll fly through the game, ready to enter the ToF, usually, around lv. 20, and picking up 300,000 xtra XP is kind of boring. (Of course, getting to the 30 is only for xtra power. It certainly is not required.)
Seriously, considering Cat Claws, Ribbons, and Fire2, 4 BMs is easier than 4 WMs.

4 Thieves vs. 4 BBs is the question that needs to be asked.

In the beginning, both of these parties are atrociously bad. However, the BBs worth increases exponentially when he reaches lv. 10.

That will put the BBs over the Astos hurdle around lv. 11 or 12, long before the Thieves will feel comfortable kicking Astos' butt.

Folowing it up, the BBs will have an easier time through the Earth Cave, but things will get hard in the ice cave and the volcano.

You see, BBs can't run, and Thieves can. The BBs are going to start dying heavily, even in the Earth cave. They'll get turned to stone. You'll have to restart over and over again.
Despite the sheer amount of higher damage, the Thieves, once they acquire the Mystic Key, will have good weapons, better armor, better running skills, and will be at a pretty high level for continuing on, since Astos was so hard.
BBs win from Astos to Ice Cave.
Thieves win from Ice Cave to Class change.

And then 4 Ninjas are really cool. If you factor in that the Ninjas can
A. Run when they have to, whereas BBs sit and take damage when 4 turns are up
B. Black Magic like FAST, which gives Ninjas the ability to do better damage against higher defense foes
C. Armor! Ninjas take it like Fighters while BBs will have the same horrible defense thoughout the entire game.

The Ninjas, although it takes 2 turns to kill Kraken, are far better because they all survive the fight, made it to Kraken in the first place, and the BBs are always walking out of the dungeon with 2 dead bodies, if they live that long.

In my opinion, 400 damage is worthless if it can only be inflicted twice against an army of 9 cocatrices or even 5 ghosts.
Imagine! 5 ghosts! If every BB strikes first, one ghost is still going to hit for 200 damage. 7 Heal potions (waste of time in the item shop), and god forbid they strike forst, or more than one hit the same BB- oh God. When I brought 4 BBs through the water tempkle, I just had to give up on keeping them all alive. It's impossible. I swear, it is the most pathetic party ever.

4 BBs is the absolute worst party. They only look better than thieves at one tiny moment of the game (not much to be proud of) because they take the second longest amount of time to beat Astos, instead of the absolute longest.