Aubameyang is a prolific goalscorer but his link up play is usually poor so he doesn't contribute a lot to the team. Also, there are numerous examples of poor attitude shown by Auba on and off the field.
Without Auba, Arsenal will be weaker in attack. I don't see how Nketiah or Pepe can be better than Auba and Gabriel Martinelli has played more of a winger role these past few months so it will be weird to slot him as striker centre again. Of course, there's Lacazette who is great at scoring but seems to lack the speed or the aggression to fight for headers. It will take time, at least 6 months, for Arsenal players to grow. Arsenal also lacks ambition. It's like they know they won't get into top 4 and they are just happy getting back to Europe with a top 6 finish.
On the financial side, Arsenal probably save around 15-20 mil by releasing Auba earlier. Arsenal has a decent squad but that's not playing to their full potential by the manager.