To me it was a TOS prequel from the start, I was expecting characters from the original to be introduced at some point, even if they end up being one or two episode cameos until closer to the end of the series where it has to at some point hand over to kirks enterprise with his crew. They are of course giving Kirk some more time than that as his character needs to be built into the kirk that will take command in a few in universe years, Spock is still young and learning to be fully Vulcan, Uhura is young and still building confidence etc etc etc.
I suspect we will get similar 2 or 3 episode arcs for the other as-yet unseen TOS crew in the next couple of seasons, I don’t know how many seasons they are planning on, but I suspect 5 or 6 considering it is the flagship show in the franchise and as a whole is doing increasingly well.