Yes, the grades of the older heroes are not accurate anymore, compared to the newer heroes. This issue has been addressed by the 7D grading crew on our website and the grades for older heroes will be re-adjusted in the near future: https://7ddgaming.com/2019/06/02/hero-grading-sheet-updated/
“Over the course of the next weeks we plan to add Ranvir’s grade and overhaul the entire grading sheet by regrading and adjusting some of the grades to current standards. With so many new and strong heroes introduced, grades of some older heroes are not as accurate anymore and hence will be adjusted. We also plan to grade 5* and 4* heroes independently. 5* heroes will be adjusted first, followed by 4* heroes.”