I think both of you are right. Being clutch and being a leader are concepts that have been bastardized by the First Takes of the world to simplify complex games. Football is a team sport, it's not basketball where one man can directly control a game at all times. The Patriots have had strong defenses and a decent run game in their SB wins. If they had been built like those early Colts teams - ie amazing offense and no defense - I'd imagine they would have been less successful.
Drew Brees is a great leader and his team respects him, but their defense imploded. Early in the season Brady looked done...due to a horrible o line that didn't give him time. The leaders and best don't always win. And there are team factors that determine your success.
That being said, teams without strong leaders rarely win it all. Brady is a master competitor whose teammates love him. Notice how he celebrates with the young guys after TDs unlike Manning and a lot of other QBs. Dude is amped up. And when you need that TD with a couple minutes to go you have confidence he can get the job done.
I wasn't a leader, sports wise. I found that my mouth would be so dry during games I could barely talk. But because I was the best player on the team my coach asked me to step up and lead. Because of my anxiety I could never really do it vocally, but I started leading by example. Usually after practice we would get some nachos and talk about video games. From then on I started working on my game after practice; I told my parents to pick me up 40min after practice ended, which is when the gym closed. After a couple days of that my teammates started working with me.
That's how I got to convince them to address various flaws in their game. We had a great pg who could drive to the rim, dish off, etc but couldn't shoot. So I worked on my perimeter defense by helping him practice finishing at the rim. We had a big man who couldn't shoot FTs so I set up a contest between us. Etc.
Now that I work in business I'm still not very verbal, but I make sure my team is on the same page and lead by example. I've played on sports teams and had job bosses who talk a lot but don't really win over the team/workers because they're an asshole or don't work hard or got the job for the wrong reasons. It doesn't work well.