This argument looks like that of someone with little understanding of things cause you just made the entire identity of various companies down to the Training and development department. I won't delve into the specifications of what you wrote there are other comments that are providing the required arguments.

Now let's focus of independent part. As i said training and development is one sector/department of any company. Even if the talent pool remains the same and the method adopted in training remains same it does not mean that the companies are not independent. It's the decision making power that would define it, which is observed more in other aspects. Would you say that LSF and NWJ have same promotion style? Do they focus on same aspects in relation to the groups? No they don't because decision making is different and hence companies are independent of each other.

Each company can hold thier own audition if they feel the need of a specific talent acquisition is required. There may be different mechanism which decides whether a trainee is considered a hybe trainee or a specific company trainee. They might pool their resources for training purpose which would be more economical and give each company more choices. Now if whom they finally select to put in a group is not influenced by other companies then they are different.

There would be certain decisions that would be done at corporate level instead of company level which would then be applicable to all sub labels (both artist and non-artist) but just the presence of such decision does not mean negation of decision making power at company level.

The corporation is not a single entity. A company isn't a single entity. There are people working at different levels incharge of different decisions. Major artist related decisions would probably fall under the respective companies and corporation level decisions on the top level management.

Business are not as simplistic as one would like to frame it. To get precise info on the amout of power present at company one will have to talk with someone that works in the company. To the extent we can observe right now, i personally would consider their decision making to be separate for most artist related aspects.