Why is it that from rank 1 to rank 2 the increase in attack and hp is 38% and from rank 2 to rank 3 the increase is only 19%?
For example corvus r1 has 23000 hp and then in rank 2 he has 32000, that is a 39% increase. But from rank 2 to rank 3 he gets to 38000 which would be a 19% increase, in other words half the increase than from r1 to r2.

5 star and 4 star always had a 36% increase from one rank to the next.