Apologies for the long response.
I am only partially qualified in that I am not a professional archeologist, but I have done post-doctoral archeological studies and have read enough archeological studies to understand the larger academic context.
It is not possible to present all the data informing a judgment in such a short work. Even in a book, it would not be possible. Thus it is common in archeology for papers to be written as part of an ongoing conversation / debate with the community - which would be defined as the small handful of other archeologists doing serious research on the same specific subject matter.
Part of that context here is that these tombs are well-established to be the royal tombs of Alexander's family, spanning a few generations including his father and his son. This is one of the most heavily studied sites in Greece for obvious reasons, and that is not something anybody is trying to prove.
In that context, his arguments are trying to identify any body as one among millions, but as one among a small handful of under ten possibilities.
At the same time, the fact that he is not a native English speaker and general archeological style come into play. For example:
"the painter must have watched a Persian gazelle in Persia, since he painted it so naturalistically (contra Brecoulaki Citation2006). So the painter of Tomb II has to be Philoxenus of Eretria" sounds like a massive leap, and it is. He continues:
"... Tomb I (Tomb of Persephone) must have been painted hastily by Nicomachus of Thebes (Andronikos Citation1984; Borza Citation1987; Brecoulaki et al. Citation2023, 100), who was a very fast painter (Saatsoglou-Paliadeli Citation2011, 286) and was famous for painting the Rape of Persephone (Pliny, N. H. 35.108–109), perhaps that of Tomb I."
Another huge leap, both 'presented as conclusions'. However he then continues to indicate these are just hypotheses: "These hypotheses are consistent with the dates of the tombs..."
So his English language use of presenting things factually does not indicate certainty in the way the words would be used in everyday speech. He seems to perhaps misunderstand the force of the terms, but also appears to be working within the context of the conversation with other archeologists I mentioned to start: They all know every affirmation is as "probably", rarely anything more. So it is relatively common shorthand of the craft in that sense.
I believe you are overthinking his responses to other authors, although I understand the culture shock. It is an ongoing conversation and archeologists tend to be blunt in their assessments. Add Greek bluntness on top of this, and it does not seem to matter to the material.
As to your last question, is this legitimate research? The answer overall appears to be yes, although I could see several points (such as the identification of artists I quoted above, and various items I noticed), which I would never have put into ink the way he did. Still, most of his arguments are compelling. It is a shame that the aggressiveness of a few affirmations detract from the overall value of his work. Archeology is not code nor is it physics. It does not pursue universal truths that are more easy to verify through repeated experiments, but unique historical ones which necessarily attempt to interweave physical details and ancient historical records. Each field has its own level of certainty, and the fact that we cannot establish these details with the same certainty as we can establish the chemical formula for water does not make them useless, or pure inventions. Far from it.