My suggestion is mainly cosmetic...
Currently there is nothing that makes champions of each tier stand out during the course of a season, how about (if possible):
1. Champions (constructors): Team gets a special livery, unique for each tier with a unique team color that no other teams but the champions can use. This changes per season to the new champions.
2. Champions (driver): driver image with champion helmet on. Option to use only unlocks when the driver becomes a champion and locks when not.
Others...
Stats: would it be possible to make sections under stats readable? For example:
1. Championships: When clicked should show what tier or tiers the championship was won & driver name that won the driver’s title.
2. Wins: driver name, circuit, total numbers of wins on each circuit won by tiers.
3: Podiums: Driver name, podium positions, number of times.
4: Pole: Driver name, circuit, lap time.
I think all these are purely cosmetic and can be easily adopted.
Some other ideas (ALL COSMETIC, I won’t suggest anything related to gameplay until all known bugs have been fixed), will add on if these are received positively ?.