Due to Jaden's abrupt movements, the majority of the gangsters had not expected that attack. So, since they were so focused on dealing with Scarlet, they could not react the moment that Jaden acted.
And in just a matter of a few seconds, many people were already sprawled onto the ground, with injuries of several degrees. But even then, Jaden made sure not to kill any one of them. Instead, he simply injured them, before progressing to attack another person.
The moment that the rest of the gangsters realized that Jaden was an extreme threat, they immediately decided to deal with him first. After all, it was obvious that the plan that they were having before was going to fail.
Since Jaden was already attacking, how could he give them a chance of dealing with the rest of the group first before dealing with him? So, they could only leave a few people behind to deal with Lucas and the others, while the rest of the group focused on dealing with Jaden.