The phrase "a formidable rival in" is correct and usable in written English.
It can be used to describe someone or something that is a strong competitor in a particular field or context.
Example: "The new startup has quickly established itself as a formidable rival in the tech industry."
Alternatives: "a strong competitor in" or "a tough opponent in".
But they have a formidable rival in Hannelore Kraft, who is leading those Social Democrats opposed to a grand coalition.
The press thus became a formidable rival in critical struggles to control what the people know and when they know it.
But he faces a formidable rival in Hamas, the Islamic resistance movement, and other splinter groups like Islamic Jihad.
But Stanford faces a formidable rival in Cornell, which is based upstate in Ithaca and already operates a highly regarded medical school in Manhattan.
Lowe's faces a formidable rival in Home Depot, whose same-store sales have outperformed Lowe's in almost every quarter in the last four years, including the fourth quarter of 2012.
If Luis Enrique's team have a formidable rival in the way of their hopes of becoming the first club to retain the Champions League, it is not in this group.
MCI and AT&T have a new formidable rival in WorldCom.
SCORECARD Down in the polls against Mr. Cuomo, Mr. Lazio is trying to link a formidable rival to an unpopular proposal, in an effort to raise questions about his judgment.
Two of New York City's major hospital organizations are exploring a partnership that would give them a large share of the city's patients and make them a formidable rival for other city hospitals in tough economic times.
But perhaps nothing could be more important to the company — and to gamers' perception of the company — than to create a formidable rival to Call of Duty in the modern shooter segment.
Foodpanda was the first, launching five years ago, but Uber Eats quickly became a formidable rival when it entered Taiwan in 2016.
