I forgot to add earlier that the walls inside the tomb were painted. As is clear from the photos, these were in terrible condition, but funerary dancing girls have been identified. I'm surprised, if the tomb was unlooted until recently, that there were not more visible traces of paint on the sarcophagus.
The keystone vault is however proving to be contentious, with some scholars questioning it's use there at such an early date in Carian architecture. The problem would then arise of trying to find a Hellenistic local ruler who was buried there. Satraps and local Dynasts continued to rule in Caria after Alexander; no 'major' ruler died there, but many Hellenistic rich private citizens erected some quite elaborate tombs, to the point where Demtrius of Phaleron felt compelled to ban them in Athens around 307 BC (a good example of such a tomb is on display in Piraeus Museum, and imitates the Mausoleum of Halicarnassus on a smaller scale).
I'd have no problem with an early fourth century date. We know that the Hecatomnids within at most a decade were hiring the leading sculptors in the Greek world, with innovations such as press-folds and piecing seen on the sculptures of the Mausoleum at Halicarnassus. Given what we know of Carian architecture and arts of the time - many people forget that Cnidus was in Caria, for example - a little innovation does not strike me as unlikely.