The same could be said about the opposite. No lanes are placed, the junior developer (or intermediate) will design a system that they are not qualified for and

The same could be said about the opposite. No lanes are placed, the junior developer (or intermediate) will design a system that they are not qualified for and the problem will be discovered only at pull-request time, when a huge waste has already occurred. Or worse, the PR will be reviewed by a senior developer that's not experienced in system architecture and will get approved. It's pretty common even in senior developers to not be experienced in system architecture, so the problem is not resolved with this approach (based again, uniquely on my experience. I didn't run any statistics)