I haven't really tried to compare GT6 to GTS like that.
And I just had a quick go at looking at GT6 Career events, as a total, and I think I counted 35 races before hitting National A.

(I may have stuffed up, my googling skills aren't the best)
So I guess it depends on what an "event" in GTSport is.
Is one event a Championship of multiple races over a handful of tracks?
Or is one event one race?
It's a tough call without knowing more details, but it's probably fair to suggest that GTSport's A-spec looks like it will fall short regarding volume of racing compared to GT6.