Really interesting article, thank you OP.
It's not surprising that 'women held central roles in Iron Age Britain' given that until the Roman invasion, what is now the UK was part of the widespread Celtic civilisation [which included the Picts, BTW], where women had different roles and could hold high status - within limits, though.
“Powerful Iron Age women abound in the texts: Onomaris, Boudica, Cartimandua, Celts with their women as judges,”
is confusing, because Onomaris, Boudica and Cartimandua are probably the best known Celtic women in history, but then tagging on 'Celts with their women as judges' implies that they were not part of the group that had their women as judges, i.e. the Celts.
I wonder why they used the phrase 'Iron Age Britain' instead of 'Celtic Britain', which would have been much clearer and more useful. 'Ancient Britons' is used a lot too in these context, which is even less useful because it suggests a direct link to modern day Britons. 'Romano-British' is another example.
It would be much clearer to refer to pre-Roman Britain as Celtic, because it helpfully signposts the reader to sources on the Celtic civilisation, culture, lifestyle, art, etc. which flourished on these islands for many centuries.