I think that depends on their strength vis a vis the state. The less powerful the state they operate in, the more brutal they can be. If you compare gangs in lawless lands vs gangs operating in lands with stronger gov, the ones operating in weaker states tend to be more violent because there are fewer resources to supress them.

Where can you expect gangs more violent, Japan or Philipinnes? Brazil or Chile?

This is faulty reasoning. Different countries have different laws, enforcement policies, and different environments, and therefore different kinds of organized crime. How brutal do you think the cartels in Portugal are?