Yes, there was no “Palestine” in the days of Isaiah. So the word that is translated there is surely more like “Philistia”... land of the Philistines.
Right and ‘Philistine’ is STILL a term of derision. Meaning something like, barbaric, inhumane or uncultured.
Some things never change
IIRC the Philistines were an offshoot of Greeks who had moved to the land of Canaan. Through their interaction with both the people groups of Canaan and with the Greeks, they taught Greece (and thus Rome and Europe) the concept of a written language based on sounds (phonetic language). Thus by days of the Roman Empire, the Philistines became synonymous with the land of Canaan in general. And the people who had been there before became known as the Phonecians.