This isn't a good article for a beginner. This isn't an article about economics, or news, or politics. This is a playful article. It is an article about language. It is making fun of the language used by regional authorities. They are using colorful, promotional language to make their regions sound good. According to the article, they are being sloppy and lazy in the way they use metaphors. You were misled by the line "Is this powerhouse a gateway?" This is a joke about mixed metaphors, or sloppy use of metaphors. A "powerhouse" is literally a place where electric power is generated. Figuratively, it means a source of vitality or energy. In a volunteer organization, someone might compliment a member by saying "She's a real powerhouse." Or, one might describe an area with a booming economy as being a "powerhouse." A "gateway" is the frame around a gate. You must go through the gateway to enter. Figuratively, cities or areas that serve as a way to access an area are called "gateways." For example, in the 1800s, people migrating westward in the United States tended to follow routes that went through St. Louis, Missouri, so St. Louis was known as the "Gateway to the West." The writer is joking about a place that calls itself both a "powerhouse" and a "gateway." The words are not antonyms. They are just completely different things. Someone who calls something a "powerhouse" and a "gateway" is just being a lazy or careless writer. They are not really thinking about their writing. They are just repeating good-sounding phrases. They are using metaphors in a sloppy way. Suppose someone said "The top banana in the company is a real powerhouse," meaning the CEO is energetic. You might joke "Is this powerhouse a banana?"

It's always helpful to include as much context as possible. If it's something you read online, it's helpful to include the URL. In this case, it is a publication whose correct name is "The Economist." I'm going to give the URL and some of the content first, so others can see it. Then I'll try to post an explanation. https://www.economist.com/britain/2022/06/09/the-many-metaphors-for-britains-regional-economies The many metaphors for Britain’s regional economies Is this powerhouse a gateway? "Since 2014 successive chancellors have touted the economic potential of the “Northern Powerhouse”, a constellation of cities including Manchester, Liverpool, Leeds and Hull. To its south lies the “Midlands Engine” which, in a feat of design, is also a “gateway to the global economy”. There is the “Golden Triangle” (whose points lie in Oxford, Cambridge and London) and the “Oxford-Cambridge Arc” (the bits between the two university cities). The “Western Gateway” spans south Wales and western England. “Silicon Fen” (Cambridgeshire), “Silicon Glen” (central Scotland) and the “Silicon Corridor” (along the m4 motorway) win no prizes for originality; Great South West wins no prize for effort."

We need some idea of the context.