I read a sentence in PONS dictionary:
Der Aufsatz ist inhaltlich gut, hat aber zahlreiche formale Schwächen.
I don't feel comfortable with this sentence construction. I know that we can omit the subject in the next clause as long as it's the same as in the first one. However, the coordinating conjunction und or aber is also omitted here which made me think it's a bad or an unusual style in written German. I would say:
Der Aufsatz ist inhaltlich gut und (er) hat aber zahlreiche formale Schwächen./ Der Aufsatz ist inhaltlich gut aber (er) hat zahlreiche formale Schwächen.
I could suppose it's more of a spoken sentence, but dictionaries in general would indicate that and would even use correct grammar then. So, I'm wondering whether this is a good/bad style in written German?