"I've heard both sides of the argument.
A spacecraft, or space rock, plunging into an atmosphere is heated to
incandescence by friction with the air, leaving a fiery [re]entry trail....Others say that compression
of the air by the leading edge of that
spacerock or spacecraft is what's really responsible for the fiery trails they leave in the upper atmosphere....
That's both sides of the argument.

Well?...Which is it?...Friction or compression?"

Compression.
I believe if you had the leading edge rough opposed to "frictionless" it wouldn't increase the heat.
Or say if you injected cold hydrogen "ahead of" your object you would reduce the heat from re-entry (not saying this would be a practical solution).