Would I be a total dick if I leave?

no

Also drop the group

Idk. Not so simple based on the little info you are giving us. If you think it may be a mean move then I would venture to say yes it may be mean. If you think it actually would be fine and acceptable then it may very well be. Not sure if this is info enough for randos on the internet to give you guidance 

before you leave an you refer me :)

*just shooting my shot here*

Have to do what’s best for yourself

I would say no bc you have to remember that they wouldn't think twice about firing you. Always take care of number one first. Of course try not to burn the bridge.

Are you leaving for a better bank or is the culture really bad or what? 

No. You are an analyst so they would drop you in a second if tables were turned. Do what is best for you. Find another offer an tell them you'll stay if you get to collect the bonuses of the 50% of analysts that left... jk

I can assure you that your firm would fire you without much thought if need be. You don't owe them any loyalty because they will always do what's in their best interest -- act accordingly.

I've seen MDs try to convince Analysts through VPs not to leave only for those same individuals to leave for better opportunities without any heads up

Your MD would do the same if they got an offer from a better shop. 

Prisoners dilemma

Do you think they'd ask "would I be a total dick if I fired him / her?"

No chance, look out for yourself. If you don't, no one else will.

Doesn't your group have some fresh blood rolling in soon off the training program? I doubt it would really hurt the team that bad. Most firms don't even have the courtesy to shoot you a rejection email after a first round interview. You're overthinking this.