Is it true a successful Team Leader or Manager is helpful to meet the company's targets?

Certainly.

no one leaves an organization, people leave their managers. So if you a great company culture which train each layer of management team, people will stay longer in your company.

If one person gets treated up unfairly in his team member experience, There are strong chances that he might do same  so Management team shall be very sensitive towards keeping a good focus and sensitization via HR that co policies are people friendly, in interest of employees , healthy work environment, opportunities to interact and share, contribute their views so they feel sense of belongings, training opportunities, good challenging work, no micro management , good reward and reorganization policy. Managers are the implementors of all this hard work of management so a good manager or team leader means a lot in growth of co

yes

Obviously i support this...............................................................................

thats obvious. who would you consider successful? a person who meets the requirements/goals established by the compnay.right? successful managers are those who make the work flow smooth to achieve the company's goals.

I am true believer that manager without leadership qualities is a useless tool.  He/she might be successful in their indvidual careers but will not prove beneficial for the organisation in the long run.  Leading by example impacts the team performance profundly.  Leader also, emphasises the human factor of his team members, and knows that there is a difference between material resources and human resources.

Never

Because, Manager may be successful as a single employee

But as a whole or as a leader, he may be failed.

So i don't agree with it