Simple systems also benefit from Amdahl's Law, but with humans instead of CPUs. This is an observation I've been trying to sell others on for years and having only modest luck. When I can show them, they get it, but you have to push and push to get people there if words fail.
When the shit hits the fan, there's an 80% chance that your most senior members will find the problem. They may find it quicker in the simple system, even, and others might get there first. But that last 20% is a very long tail, and even longer in a complex system.
In a complex system, many of your members cannot participate in the triage process, because they don't know enough to know what's relevant. They slow down the people trying to work the problem trying to learn new things (good) or offering low-probability scenarios (bad).
There is no 'All Hands on Deck' scenario for the complex system. To be responsive, you have to kick some or even a bunch of people out of the room, and once they leave they can't really participate.
The first phase of a triage is getting a tight repro case. Many avenues are blocked until that happens. And some people have a knack for repro cases but aren't so great at debugging. With more people you get a higher quality repro, which cuts a lot of time off the rest of the process.
Part of debugging is the cost of the verification versus the likelihood. Simple Systems afford the opportunity for people to test out unlikely but plausible scenarios that are in the long tail, without distracting from the more 'boring' checks already being done.
And when bugs are identified prior to deployment, a simple system means you can hand the repro case to the responsible party and expect/demand that they get their fix on the first try.