Do Undergrad Extracurriculars Matter in MBA Applications?

The "leadership" thing is a bit of a smokescreen. Not that it's unimportant if you have it, but if you do a flyover of LinkedIn profiles of current MBA students at H/S/W, it's not like it's teeming with world class leaders who have supervised armies of employees or volunteers (yes a few may have, but they are in the minority).

But what IS the more common denominator?

Most of them went to top schools in their respective countries. In the US, that's Ivy/Stanford/MIT/Duke/Cal/UVA/Mich/Texas/UCLA, and add in the 7 Sisters a few lib arts colleges, and NYU/Northwestern/USC, and you basically have your American contingent.

A lot also worked at top tier firms for a bit - not necessarily their current employer, but they spent at least some time at a bulge bracket or top boutique, MBB consulting, or Google/Facebook/etc. Or if it's non-profit/public service it's Teach For America, IMF, World Bank, IFC, etc. Basically large organizations that are established AND selective in their hiring practices.

They also have solid GPAs and GMATs.

That's really the big 3 (college pedigree, some time in an exclusive global firm, and solid numbers). Those 3 alone won't get you in (as there's plenty of folks who don't), but that pushes the needle forward more than anything else. Also, it's not necessarily because the adcoms are brand whores, but that these things are harder to "spin" - you either worked at McKinsey, or you didn't. You have a 760 GMAT, or a 680. Your GPA is strong, or it's not. You went to Princeton, or you didn't.

"Leadership" is a bit of a nebulous thing anyhow especially for folks in their early 20s. Rather than preoccupy yourself with that, focus more on doing a deep dive into group activities that you LOVE. Causes that you believe in. Find your community of like-minded people outside of work (if you have time outside of work) to make a difference. It's real easy when you're working full-time to just spend your free time kicking back and doing nothing (or just being hedonistic - i.e. indulging in expensive social things, vacations, buying toys, etc) but the high achievers are those who spend their time growing and learning and staying engaged in organized group activities that they believe in (and that they find fun - but it's productive fun). It's not just good for applications, it's good for your life. If you are staying busying outside of work, even if you have relatively little free time, but use that free time to stay productive and growing - you won't have to "spin" anything in your essays or interviews. You don't have to search for "leadership opportunities" - they will more organically come up when you're deep diving into group stuff that you love to do regardless (i.e. the more involved you are, the more skills and experience you develop in that group, etc - the more leadership opportunities will naturally come up).