Mumford & Sons close out the first weekend of ACL Fest on Sunday, Oct. 2, 2016. Contributed by Charles Reagan Hackleman

How big is British folk-rock band Mumford & Sons in 2016? As a final-night headliner at the Austin City Limits Music Festival, they were a heartfelt favorite for many who crowded near the front of the stage. But a noticeable thinning-out after the first hour told part of the story.

More of that story is in their record sales history. Last year’s “Wilder Mind” went gold but came nowhere near their debut’s triple-platinum number, though the advent of streaming clearly has a lot to do with that.

“Wilder Mind” may have alienated some of the band’s core fan base, as the group steered away from its hallmark traditional-roots approach toward a more sophisticated range of rock and pop textures. That was probably a good thing, judging from Sunday’s show. Early on, the band members made frequent switches between acoustic and electric instrumentation, adding another dimension to their performance that helped keep the show lively and intriguing.

It’s not like these were sudden left and right turns, though. Whether lead singer Marcus Mumford is on acoustic or electric guitar, whether Ben Lovett is on a real piano or synth keys, whether Ted Dwane is playing upright or electric bass, or whether Winston Marshall is on banjo or guitar, the Mumford & Sons aesthetic melds the newer and older material together.

That aesthetic is both a vital part of the band’s identity and a limitation to creative development. The template is pretty clear by now: Most Mumford songs begin subtle and calm, then gradually build into an intense and dramatic (often melodramatic) release point. Dynamics in music are essential, but when they’re used too often in the same manner, the effect can be deadening.

Still, the faithful stand by the band, especially when their favorite songs roll around. “Little Lion Man,” batting second in Sunday night’s order, quickly brought out crowd chant-alongs, and “The Cave,” a little over an hour in, got packs of fans both singing and pogoing a long distance from the front of the stage. They saved their biggest U.S. hit, “I Will Wait,” for the encore; it hit with comparatively less force, mainly because many had headed for the exits by then, perhaps trying to beat the mass exodus with Monday morning coming down.

It’s worth noting that two of the band’s most adventurous tunes came when Mumford took over on drums. “Lover of the Light,” from 2012’s “Babel,” was fleshed out even further with the addition of trombone, trumpet and fiddle; and “Dust Bowl Dance,” from 2009’s “Sigh No More,” closed the main set with an inspired maelstrom of barely controlled chaos.

The band spiced up the encore with a new number titled “Forever” along with a well-chosen (and well-presented) cover of Bruce Springsteen’s “I’m on Fire.” Clearly those fans who have stuck with Mumford & Sons from the beginning went away satisfied. Whether the band can remain at the level of ACL Fest headliner in the years ahead may depend on them broadening out not only their sonic approach, but their songwriting vision.