This is absolutely incorrect. A player's ratings drive his performance in OOTP. Here is a quote from the first sentence of the
Player Ratings section of the OOTP 21 manual:
Player ratings, combined with the game engine and its use of league total modifiers, is what drives all statistical outcomes.
The stats you see in the player editor are an estimate of the resulting stats that the player would generate with his ratings in a neutral, modern Major League environment. Those stats do not impact results in OOTP in any way, shape or form. They simply show what the game estimates the ratings would produce for that player under those specific conditions.
As the
Player Editor section of the OOTP manual explains in the definitions of Resulting Stats under the Offensive Ratings Editor section:
There are buttons below those stats in the player editor that allow you to enter stats and then ask the game to create new current player ratings or new potential ratings based on those stats. That doesn't mean the stats are "driving" anything. You're just asking the game to create a new set of player ratings based on a goal of the player hopefully performing at around that level in a neutral, modern Major League environment.
Ultimately, player ratings drive everything, although there is a "top-down" effect from the league total modifiers, which is what governs the overall statistical output of players and the league, This is to make sure performances are in line with the given era of baseball, tendencies for that year, etc.
Now, when you're playing historical games, OOTP uses a player's real life statistics in the historical database to create his initial ratings based on the range of years and settings you specific. It may also update his ratings if you've set up your game to recalculate ratings after each season according to stats in the database. But these stats are then converted into ratings, and the ratings, game engine, and league total modifiers drive all outcomes.
As far as player development goes, I'm not an expert in that area, but the development engine handles all of it. Especially if you're using the coaching system, spring training and minors, there are certainly things you can do to help players develop better. But, to my knowledge, it's only their potential ratings, your decisions, any coaching and training, and the development engine that determine how quickly or how well they develop. But only their current player ratings, the game engine and league total modifiers will drive their actual statistical performance.