Committed Hero
Hero
GURPS' combination of skill defaults (ie, letting one skill stand in for another at reduced efficiency), plus the way it charges more XP for more complex skills, colors my answer.
I feel like it's a sensible rate for academic skills being studied in a calm situation with a lot of time doing other things, but a rather low rate for practical skills being used in real situations on a daily basis. For example, people in WW2 went from never having flown a plane to the greatest pilots on the planet, capable of incredible feats, in a lot less than 4 years.
Traveller's inability to distinguish routine (which teaches only slowly) from high stress/high activity environments is one of the many things I hold against what could be a really great system. The way the CharBurner works should not necessarily reflect the most intense possible training, either focused or "on the job". It's fine to separate the mundane from the unusual or the heroic.
I asked Qwen: if you use the 5th edition of Dungeons and Dragons and you scale it towards real-world realism of skill development, what is the highest level a fighter could reach?