"Fast Trainer " & a "Fast trainer" that will have consistently good ratings. "
Here we talk about 2 things, training speed, to increase the skills of the player, and, contribution, what the player give you during matches.
A player can be programmed to, have a better ratio scoring goals as min/max in the sense that, you can have 2 ST's, been exact players, same stars, foot, weight, etc... but one, will score 40 goals in a season, and the other, 4, and both can have 5*. And this one who scored 4 goals you can train him 5 stars till 9, but, as there is a ration of min/max of contribution and capability, never, will score with 9* the 40 goals that scores the first player that, have 5*.
Usually, good players, these who are key players and do a good contribution, tend to be Man of the Mach and have good ratings, 9's 10's, and this, in the end, is what count. Contribution, contribution, contribution.
Too, a bad aggressive player, really can ruin a team, one can feel sometimes (at least I do) when a player comes to the field or leaves, and the team performance suddenly fall. But thats another thing, more deep really.
Now ma suggestion is,
1-contract fast trainers
2-take a look at the team stats page, if, for 5*, 6*, 7* or 9* that a player have, dont work, dont work and thats all and sometimes is better sell a 7 stars player, that dont appear in the matches, and try with a new, 5* because, and this is another point, a single player can win for you the 70% of a title.
So all can depend of 1 good player really. Think in it.