The important thing to remember is that BRT, like LRT, is very diverse in its implementation. What I am referring to is true BRT, which only a handful of systems nationwide are. I've seen BRT labelled as such when I just shake my head, because some "BRT" services are just regular bus service with maybe an express design. Light rail has many forms: trams or streetcars all the way up to mostly grade separated with rights of way such as Calgary's C-Train, with relatively heavier vehicles. Its hard to paint things as black or white.
The HealthLine in Cleveland is BRT done correctly, it feels professional grade when you stand up on the platforms and enter the vehicle at floor level from the platform, you realize this isn't 'just a bus'. The articulated length allows for up to 100 people per bus (I think that's the capacity, may have to check), which is plenty for a line carrying 15,000 a day. Before I experienced the HealthLine, I was much like other people in thinking BRT was really a second rate, not worthwhile investment.
In terms of Nashville, a city I grew up near and spent years in, I hope they get the BRT system right there. Considering the corridor they are implementing it on, its a proper and necessary plan. However, the Koch brothers got involved and tried to get the BRT killed. Now they are having to rework the BRT and use fewer dedicated lanes outside the central core to match what the state is forcing the local government to do. At least the state came to an agreement to allow it to go forward instead of following the radical anti-transit agenda of the Koch brothers. Its a case more transit planners need to be aware of, since its a gross over-reach of right wing politics in an environment they have no business getting involved in.
I've even made pretend maps of Nashville before, with what a $1 billion BRT investment would look like:
If you spent $1-2 billion in BRT for the city, you'd get almost 50 miles worth of good, quality, frequent transit services in the most urban corridors. Each of these choices reflects major business, retail, and housing hubs. This would also allow traditional buses the ability to run in a more circular pattern around Nashville's built form, complimenting the entire region. This theoretical project would compliment the existing built form by terraforming existing city streets with desperately needed updates and upgrades. Just the new concrete, pavement, and landscaped look would improve the city immensely even for those who don't use transit.
FYI, if you want to know why I didn't draw a line northwest, the city pushes against rugged Appalachian foothills in the northwest region, its very low population density. The river to the west also forms a very depopulated region along its industrial and floodplain region. If you built this map with light rail, I wouldn't be surprised if you'd be talking about a $10 billion investment for a city that wouldn't have ridership to support it.
This is the type of environment that BRT makes the most sense: making an auto-centric city transit friendly, with a full compatible circulation system and minimizes transfers. You could get virtually anywhere in the region with 2-3 transfers at most, over a vast area.