ES6 has some nice features -- all other things being equal I'd chose to write it over ES5. Or even ES3, since it fits with that sloppy ageist accusation you tossed off.

As soon as you say "Babel" (or another transpiler), though, all other things are not equal. I've already chosen to work with ES6 anyway in some circumstances, but honestly, when it comes down to it, the benefits are marginal enough over ES5 that there's a reasonable case that anyone already effective with ES5 doesn't need to transition.

And I might even go so far as to speculate that a programmer who is unable to be effective with ES5 might simply be the kind of programmer who can't really be effective whether they'd be working with Python, Ruby, Go, C#, whatever... but that would probably be tenuous bullshit on par with assuming anybody who doesn't want to add a transpiler to their toolchain in order to do essentially the same things they can do without it is Just Too Old.