It is just bigger than altcoins, not more secure.
That's total junk. Thousands of people have attempted to roger Bitcoin in every way possible and it's still rolling. I don't think the same can be said for many or any alts. If they were actually put to the same test there's no way of knowing whether they'd wilt immediately.
It is rolling until few known pools and few known major miners are confronted by guns and black copters or are simply prevented from accessing Internet (trivial). At that time you'll love if you have a stake in something less centralized, like well-distributed PoS altcoins where hundreds of mostly unknown people are running the show and are in many cases actualy using the same secure code as Bitcoin excluding the gimmicks.
One bank, one leader, one exchange, one coin, one whatever means a single point of inevitable failure so good luck with Bitcoin only.