You can't really lump these together.
Broncos was deliberate. Brisbane actually consulted with the Denver Broncos. I think in-part to win a bit of mind-share from NFL fans if/when they take a look at Rugby League.
Raiders and
Titans are likely copied.
The
Cowboys and
Steelers are obvious copies, but fit the identity/culture for those areas.
but...
The Penrith
Panthers (1967) pre-date the Carolina Panthers (1993) by a 26 years. There is also a reason for calling the team the Panthers. The "
Penrith Panther" is myth akin to the "
Jersey Devil".
The Redcliffe
Dolphins (1947) pre-date the Miami Dolphins (1966) by 19 years. The Redcliffe Dolphins are not the NRL team, but they are putting up all the money, and it is their brand. They would be mad to have a different nickname just for the NRL team.
There is no NRL team called the
Saints. The St. George team takes its nickname from
The Legend of Saint George and the Dragon. The St. George Dragons pre-date the New Orleans Saints by 46 years.
and...
I'm not sure the NRL would allow a team to pick a name like the
Rabbitohs these days, but if they did want more of that I'm all for the NZ team changing their name to the Possum Trappers.