The truth is somewhere in between. Other fields of economics do not have their own departments. There are no labor economics departments or IO departments, but there are finance departments. So no, finance is not just a subfield of economics. It is a very closely related field.
In terms of the quality of the journals in the two fields, I have always thought that it's better to look at papers than to look at journals. There are dreadful pieces of work in the AER and mighty fine pieces of work in the JF. That said, the lower down the food chain you go in both economics and finance, the more your department will glorify lousy journals. It's not just a finance-specific thing.
This. Other academic fields in Econ don't have their own deapartments.
Also, in the real world, accounting and finance are often in the same departments within businesses (both considered shades of bean counters), while economists are dumped all over the place, and have to add more practical skills to be of any value (e.g. learn taxes).