First off, as of 2007 AIG, Bear Stearns, and friends were in the center of a large, complex web of interlocked investments, contracts, and creditworthiness assumptions. Billions of dollars in value were declared to be "safe" and used as collateral for further leverage, effectively laundering them of their inherent riskiness. When this web collapsed, it happened all at once. Today's fintech firms run the gamut, but by and large they consist of proprietarily-managed, non-traded funds. There's none of the securitization that allowed risk to creep outward. The result is that a failure in one is less likely to trigger a failure in the entire system.
Secondly, consider whose wealth fintech is managing. If fintech were managing hundreds of billions of dollars of money belonging to people, institutions, and other banks, it'd be cause for concern. But if the marketing of funds like Betterment and Wealthfront are any indication, they're targeting individual investors. Naturally, individuals losing money is a bad thing and would depress demand and confidence for a while, but it's a far cry from the catastrophic, systemic credit crunk we experienced as a result of the crisis.
Finally, just because a system is automated doesn't mean it's going to rogue. Just because an algorithm is complicated doesn't mean it's fragile. I appreciate (and to a certain degree share) the anxiety, but I think it's misplaced in this particular case. This article seems to be to be more about hand-wringing about computers doing things than actual commentary about the structure of the financial system.