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You're missing the point: We (GP and I) don't think you need known actors. There are great series with (then) unknown actors. It's just strange to have such a massive budget (which usually would go, in part, to known actors and directors) and then forgo them. Also, for directors, there's definitely a case to be made that you need someone who can handle such a large budget. That's why I made the example with the junio…
Yes, some of the best titles have none or just 1 top tier actor at the time: Star Wars (Alec Guinness), West World (Anthony Hopkins), Game of Thrones (Sean Bean), Breaking Bad, The Wire. I'm sure there's other's I can't remember. Some directors prefer fresh actors for some movies. It s not necessarily a red flag, but it could be. Time will tell.
West World had Ed Harris, Evan Rachel Wood, James Marsden, Thandie Newton, among others. These are mid tier actors that are quite well known (even though they're not superstars).
Breaking Bad had as its lead a very prominent television actor in Cranston. Malcolm in the Middle was a hit tv show that had a long run as far as TV shows go. He was already very TV-famous prior to Breaking Bad. Getting Cranston to carry Breaking Bad was them going with a TV heavy-weight with tons of experience and a deep familiarity for TV audiences.