Ok, my last words in this topic

First of all: Native North Americans or Mapuche never had an empire too. Is that mean they shouldn't be playable civ?

And now ad rem. I have used Rome's example with reference to the territorial argument. Of cause, Rome is not comparable to The Celts. But The Romans are a good example when it comes to make a distinction between one's Nation/Culture and it's heritage.
Cultures and civilizations are developing over time, mixing, absorbing each other. Modern France is mix of Celtic, Roman, Germanic cultures, and their own later great achievements. All this makes them unique: not Celtic, not Roman, not germanic but French. The same as the Irish, Scottish, Swedish, Norwegian etc. They are all unique but also they have their cultural heritage. We don't say that the fact French civilization has roman origins excludes The Romans as a Civ. We don't say The Romans would be a blob Civ because Spanish, Portuguese, or Italians have Roman origins too. But we are saying The Celts are covered by modern Scotland... Why?
This is not a case for the Romans because we feel that Roman civilization is not a French one.
When it comes to The Celts we are mixing this and somehow we expect that ancient Celtic heritage is not a distinct culture, but it is part of Irish, Scottish culture. This context makes us perceive them as a wide umbrella. But try to think about The Celts this way: They were European Iron age civilization who was fighting with Rome. Heart of their culture was in today Switzerland and Bavaria (some theories claim the source of their culture are the Pyrenees), from where they expanded to Portugal, Turkey, and Britain. Brennus conquered Rome before Romans built their empire. Their heritage is druidism, warfare culture, mining, trade, calendar, craftsmanship, a proto Celtic language etc. But they lost. They lost with Rome and later with Christianization. Today splashes of their heritage survived in some cultures but they do not exist as a Celts. This kind of perspective on a Celtic Civilization doesn't mean they shouldn't be named The Celts or they are blob there. And Civilization game is also about it. What if. What if The Celts were never conquered? Wouldnt you like to try it in the video game? I would like to.