Original F1 cars start at around 600. This is too low a baseline, as they are slower than real F1 cars. Even the best drivers perform worse in TT races than in real life (e.g., at Silverstone).
The starting point should be around 850-900. However, after a few seasons , there should be an upgrade reset (a significant change to the technical regulations, covering all four upgrade areas and the power output of individual engines). After that, the level could drop to the current starting point (around 600).
This would increase realism and make the career more engaging.