Roof rack options - rails or no? 2019 CX-9

What is the advantage to having roof rails to attach cross bars to as opposed to buying just the cross bars that use mounts connected directly to the mount points (where the rails would attach)? My '19 didn't come with the rails - and the oem rails are pricey. Was thinking of going with the Rhino Rack, which may be easier to remove when not in use.
There isn’t much advantage to the rails. In theory if you could find bars that can easily be moved to any location on the rails, this would give you flexibility in where to put the bars, but i all the bars i have seen have very specific mounting locations on the rails and cannot be moved around. Maybe some exists, i don’t know.

I am also not sure if there are compatible bars for the cx-9 that mounts without the rails. But if there are some then i don’t think the current rails would add any real advantage unless you can one that can be moved around like i mentioned above.

Funny thing though, as expensive as the mazda rails and bars are, they were still cheaper than the equivalent from thule and yakima when i was shopping around. So i went with the mazda rails and bars.

Also the mazda bars are curved, so not ideal if you are looking to carry large flat items.
Just had a look at the rhino rack you mentioned. The only issue i can see is that in a 2 bar setup you have to use the 2 front and mid mounting point. It looks like a bit of an awkward position for the bars, because it is pretty far forward. (Look at the position on the instructions here:

Also ask about the height of the bars on the roof. Low bars look sleeker, but if they are too low, it causes issues with your load touching the roof (or the mounting hardware for your accessories) and can also hit the rear antenna.
And for comparison sake, here is where the mazda bars are: