Sue β Wales did not have quite the same status as England, Scotland and Ireland, being, as I understand it, a principality within England. So Wales was already included by showing the English rose. The inclusion of the Welsh leek would have produced the strange anomaly of including Wales twice! Even the apparent leeks on the black three-footed patriotic vase attributed (possibly erroneously) to Davidson shown on p29 of Notley/Miller's may be just artistic infill of a slim vertical panel rather than a deliberate attempt to include Welsh leeks. The same reasoning explains why we do not see symbols for the Isle of Man and the Channel Islands β the English rose already encompassed them.
Whatever the faults of our Victorian forefathers, and there were many, their logic here was impeccable and accurate. ... and, unless the status of Wales has changed in the last century, it is our use of these symbols today that is confused and inaccurate.
As for your final point about sexist or otherwise discriminatory language, I thought the more irrational extremes of this had all but disappeared a couple of decades ago. It has not helped having little serious published study or guidance. A rare and useful rational essay on this is contained within the final chapter of Bill Bryson's Made in America
, well worth reading for a variety of reasons connected with the English language.
I myself have a problem with the use of correct language as I am working on the publication of the 1863β66 diaries of Joseph Brookes, a humble Northamptonshire village Parish Clerk and shoemaker. Joseph describes himself as both a cripple and as crippled, perfectly correctly then. The words have only acquired their derogatory connotations in the last half century or so. Am I to bowdlerize Joseph's beautiful language? Of course not, though I will, no doubt, receive a few complaints.