The British East India Company benefitted frm the Mughal success because those successes made it easier for the company to take over more of India when the Mughals failed.
At the height of their power, the Mughals controlled a great deal of India. This meant that all of that territory was ruled by one authority. This was helpful for the East India Company, but not until the Mughals failed. As the Mughal Empire weakened, the company and its armies were able to defeat them. This meant that the control over the Mughal lands passed to the company.
In short, then, the Mughal successes sort of packaged much of India up into one state that the company could take when the Mughals failed.