Yes, that's a good point. But it's hard to trace back when a tribe or a union of tribes becomes a meaningful entity and 'a people' and that's why we usually refer to an official founding dynasty. It's like tracing back the origins of a language - the more you go back, the less defined and characteristic it becomes.

St. Andrew preached the gospel in the Black Sea region in Thrace around modern day Varna and Sozopol.

Yes, that's a good point. But it's hard to trace back when a tribe or a union of tribes becomes a meaningful entity and 'a people' and that's why we usually refer to an official founding dynasty. It's like tracing back the origins of a language - the more you go back, the less defined and characteristic it becomes.