To be fair, "warp capable" has never
been a criterion in the application of the Prime Directive. That's pure fanfic.
I guess some episode writers might believe that warp capacity matters, but no episode or movie has actually featured a reference to warp capacity mattering. TNG "First Contact" had contact coincide with the launch of a planet's first warp experiment, but other episodes featured contact with species that did not have warp drive.
The "internal matters" aspect is certainly part of the PD, though. DS9 itself establishes in "The Circle" that it's the PD specifically that stops Starfleet from interfering with the civil war on Bajor, at least until the complicity of aliens (that is, Cardassians) is verified.
Whether a conflict involving Bajorans, Prophets and Pah Wraiths would involve sufficiently many "alien parties" to disqualify it from PD protection is a matter of interpretation. The tech levels of those parties should not enter the equation, though.