The problem comes about because the first class teams are filled with players that are rated between 65-75. However if you look at the ratings on the club standard players that you play with and against then you will see that there are 3 or 4 in every club side that are rated 60-65 and are improving at a similar pace to your career player.
As a result each first class team has a larger talent pool available of players that are 60-70 and as a result these get called up into the squad when your career player goes up.
To overcome this you could increase the ratings of all of your first class players to 70-80 but then you would create the same issue between the first class team and the international team. Meaning that you would have to increase the international player values in order that they keep their place.
Eg: James Vince (England squad player but not 'featured' in the game is rated 65 I think. So as soon as players get promoted from club cricket to Hampshire he loses his position of captain and then his place in the team fairly quickly. You could overcome this by boosting Vince and the other Hampshire players to 75-80 - but then the England team will get filled up by Hampshire players who are rated higher that the England squad players. So you can increase the England sqaud ratings to 85-95.
All this is bearing in mind that the best players in the world (Smith, Kohli, Root, Stokes) are generally rated at circa 85/100 to start with. But if you bumped all of these to 95/100 then presumably it would have a knock on impact on game play and scores.
Ideally the best club standard players should be dropped from 60-65 t0 45-50. However we are not able to edit these stats as the club sides are auto-populated at the start of the mode. Hence it will need Big Ant to resolve.