I don't think you necessarily need to enjoy the books you dissect. It helps, but I don't know if it's necessary. Plenty of people succeed because they write the book they can't find. They write something that's missing from the market.
It is important to understand what readers like about a subgenre, niche, or trope. If you can understand what readers like and why, you can deliver that, even if you don't like most of the popular books in your niche.
It's much easier to do this if you also like the subgenre, niche, or trope. So I do recommend picking subject matter you like. But it's not strictly necessary.
I don't really get billionaire books or billionaire readers, but I've done really well with my billionaire books. Because I focus on what I do get or I find a way to get it. I tell everyone I found a way into my first billionaire book, a fake marriage book, via The Hunger Games. The first half of THG is also about a determined girl from a poor family thrust into the world of the rich and powerful, made over and fawned over and unable to know what's real and what's fake.
You have to find a way in.
Now, I don't really agree with your breakdown of trends and writing to market. I think you need to spend more time studying the romance market. This is knowledge that comes with time, which is where people who aren't genre readers are at a disadvantage. Looking at what is selling this month tells you what's popular now. Looking at what's selling this month, every month, for five years tells you what sells over time.
With romance, and probably with any genre, you can just... ask. People will tell you what sells on the regular. I always tell people to look at the midlisters, because they're the ones selling based on the quality of the package. Don't get me wrong. Big sellers need to entice readers too, but it's easy for new authors to see a big seller's flop as a success. I'd call myself a mid-lister, but my idea of a flop looks pretty good to a lot of people.
How you'll dissect books and tropes really depends on your temperament. I'd suggest reading at least three books in a given niche. You don't need to enjoy them. In fact, a lot of people have a hard time enjoying and dissecting at the same time. But I find I can't really do this if I actively dislike the book.
I always suggest writing evergreen when writing to market. It works better for most people. It's safer. It's a smarter way to build a career.
But there is a lot of money in writing to trend. It can work very well, but it's much riskier. If you get to a trend too late, you might totally miss the boat, and your book will be a much harder sell. Last year, reverse harem was huge, and a ton of people sold a lot. Now, very few authors are selling reverse harem. I don't really know how well people's old reverse harem books are doing, but I'm guessing 90% of the authors who jumped on the trend aren't seeing big sales.
I wouldn't recommend it unless you're a very fast writer who likes a high risk, high reward scenario.
It is hard to know how far to zoom when you're new to a genre. It takes practice and study. I'm not sure there's a shortcut. In romance, there will always be room for billionaires, bad boys, blue collar heroes, small town, romcom, erotic romance, BDSM, rock stars, mafia, sports, family saga, and dark romance (not a comprehensive list). But they might require different packaging. In 2016, there were a lot of books with "bad boy" in the subtitle. Now, there are almost none. And they will go in and out of fashion. Sometimes, they will be easier sells than others. My rocker books used to sell a ton. Now, they're a much harder sell. I still have diehard readers who want more. I could do okay with a rocker book, but it's not as big right now, so the ceiling isn't as high right now.
Right now, sports romance is huge. This is a niche that always sells, but I expect, in a year or so, it won't be as easy of a sell.
Part of this is market saturation. When there's a need, authors rush to fill it, they overfill it, it gets harder to sell. Romance authors are fast and business savvy. They will fill any hole in the market very quickly.
TL

R As usual, I'd recommend Chris Fox's books, and especially Writing to Market for more on this.