Without commenting on the corporate governance side of things, being vertically integrated at Samsung's scale has a lot of advantages - boosting the profitability of the phone division at the 'expense' of the battery and display divisions probably unlocks more "shareholder value" in the long term than having the individual divisions finding their local profit maxima as separately listed companies.

It makes sense for the high-margin divisions to 'subsidise' the low-margin-but-strategic divisions. It also makes sense from a vision perspective - "here is the ideal phone we would like to sell in 10 years, all divisions, do the necessary R&D to make it happen"