I mean yeah the playing sounds a bit different since he plays differently compared to Brad but Given Up sounds mostly the exact same from when they played it back then. However, I did notice a lot of the amp effects they use sound a lot different (worse in some ways) which could be that.
Also the mixing for the shows recently has sucked compared to previous years (especially when Pooch was around was probably the best LP has sounded good live). On some songs the bass is super loud, guitars are mixed low, vocals are turned down or Colin's drums are louder than everything else. They also seem to always have IEM issues as Emily and Mike are constantly adjusting their in ears.
Benjamin still works for LP, same goes for Mike's guitar tech. However, Dave's tech who's been with LP since the Meteora era I believe (Ted) isn't with the band anymore.
I don't think it would be good for Ben to play every single show as he would also have to tech for himself (go off stage to grab guitars etc) when Brad would miss shows. It's better to have someone like Alex to fill in.