It’s no surprise Mariah Carey is headlining arenas — the singer plays the TD Garden on Monday. Carey spent much of her life being the biggest pop star in the world.

Pop culture has a selective memory, but in the decade between the heyday of Madonna, Michael Jackson, and Prince and the rise of Britney Spears and the Backstreet Boys, Mariah ruled. And nobody was close to her: 19 No. 1 hits that spent 90 weeks at the top spot and a whopping 220 million albums sold (equal to Prince and Britney’s totals combined).

So yes, she gets to headline the TD Garden, Madison Square Garden, and any other gardens, arenas, centers, forums, and fieldhouses. Only when Mariah takes the stage in Boston, she’ll likely only sing three of her chart toppers in their entirety. Instead she’ll stuff nine of her hits into a 13-minute medley and devote the remaining hour and change to Christmas carols. This is just what the people want: Why hear “Emotions” in full when you can hear the hundredth version of “Here Comes Santa Claus (Right Down Santa Claus Lane)?”

Slowly, steadily, Mariah went from being a vital part of the pop ecosystem to the queen of Christmas, camp, and relentless cheer. Back in 1994 her song “All I Want for Christmas Is You” was a little novelty, something as inconsequential as a cut from “The Taylor Swift Holiday Collection” or Hannah Montana’s take on “Rockin’ Around the Christmas Tree.” Then “Love Actually” happened.

“All I Want for Christmas Is You” snuck into seasonal playlists after being featured in the 2003 holiday film. Each year Mariah’s signature song has snowballed (kinda nuts to think that you can have a tune spend 14 weeks at No. 1 and win two Grammys, see “We Belong Together,” and not have it become your signature song). In 2012, “All I Want for Christmas Is You” cracked the Top 40 for the first time. In 2017, it made the Top 10 for the first time. Since 2019, it has gone No. 1 each year.

Estimates vary, but the song has made the singer in the neighborhood of $100 million.

Now, it must be said, it’s a very, very good pop song. But is it better than “Fantasy” or “Always Be My Baby.” And, more importantly, is it better than Wham’s “Last Christmas” or Darlene Love’s “Christmas (Baby Please Come Home)” (maybe and no, respectively).

Now, what’s better and what’s worse, clearly doesn’t matter. Mariah seems thrilled with her transition from pop princess to Christmas queen. Of course, being thrilled is integral to Mariah’s brand.

The last time she played the Garden singing straight pop songs, in 2017, she opened for Lionel Richie.

Now Carey will sell out arenas as long as she wants as long as she is doing 90% Christmas songs. But should she be defined by the holiday? Carey, fans, executives, and Google scream yes (search her name and digital snowflakes fall down the results page).

Despite that trademark, relentless cheer, there’s something a bit sad about all of this. Well, as sad as $100 million, a couple billion streams, and a hit on track to become the biggest song of all time in 2024 can be.