You can just cast fly on a regular rhino. The weird rule interaction is for giving the rhino wings, but it's still pretty balanced for where you can do it.

Also, this has convinced me to add winged rhinos to my campaign world. Wingless rhinos are the weird thing now.

A flying rhino? Such a weird situation! We should name a junior high school after it.

It's already a celestial, a fey, or a fiend rhino. Given that, having wings isn't surprising.