There are a lot MORE people who get B or C than A/A+ on titans, so more total ascension material rolls happening in those groups. That’s why it seems like there are a lot more people getting 4* AM at C than at A.
If there are 5 people at A/A+ on a 12* titan, and 10 at C:
5 people x 4 rolls per person = 20 rolls
10 people x 3 rolls per person = 30 rolls
So each individual with a C has a worse chance than each individual with an A/A+, but there are more total rolls distributed across all C than across all A/A+.
That’s why it’s more likely that you’ll hear a C say they got a 4* AM than an A, even though your personal chances for a 4* AM are better as A than as a C.