Just for fun, if we assume that the TEF is the same in games, like lvl 1 drill?, and a game takes 25% fitness, it basically breaks down to something like this for a fast trainer that we do not use any Rests on (and I am tired so need to think this through again tomorrow.... ):

-TEF for a 7 star FT (lets say this player has 120% ability in Day 1 of a season) -- 0.11

-Fitness ability recovery during a season -- 24 hours/day / 3 hours in between recovery * 6 % = 48%

-Fitness loss per game on avg -- 24%

-Games played during a season (app) -- 52 (its basically possible to play all games)

Total gain in Ability% a season = 52 games x 24 Fitness% * 0.11 = 137 Ability%

Total gain in total ability = 137 Ability% / 15 abilities = 9.1%

This would mean that it would take around 125 Rests to get that player to 140% and 8 stars on the last day of the season (age 18-21). Meaning that you can basically keep 6-7 players at 8 stars with a ambitious zero buying token budget if you do not power-train any players and use all rests on maintaining ability.

Another interesting conclusion is that its always better to rest a core player as much as possible and train him with lvl 4 drills instead. As a reference point, if all fitness recovery goes into lvl 4 drills instead of games -- ie 48% * 28 days = 1.344 -- the 7 star player would gain 1.344 * 0.14 =188 ability% or 188 / 15 = 12.5% in avg. ability instead. Interesting! Will look more at this tomorrow if I get time!