Well, he alternated between not believing in the existence of (EM) radio waves at all and claiming that they were useless for transmitting messages, which isn't

Well, he alternated between not believing in the existence of (EM) radio waves at all and claiming that they were useless for transmitting messages, which isn't the same as the luminiferous ether idea. Belief in a luminiferous ether (that fills all of space) is consistent with the idea that EM waves can travel through space (after all, we can see light coming from the Sun, etc.) and that radio waves could be used. But Tesla seems to have argued that working "radio" technology was really electrical currents traveling through the ground (or through the ocean in the case of radio on ships), which then somehow induced "reception" in the radio equipment located above the currents.