The valvetrain and fuel injection systems of any given internal combustion engine vehicle made since the 1980s are far more complex than the voltage controller of an EV drivetrain. The difference is that those mechanical components are in a system that can have multiple minor fail states before ceasing to function and contain far less energy than what's coursing through the voltage controller. The reason EVs are more dangerous currently is because they haven't gone through the decades of regulations and testing needed to provide multiple diagnostics and failsafes the way mechanical components have. That's easily fixed by just giving them a few years and letting people develop folk knowledge they way they did with internal combustion engines. Even now hobbyists are developing new ways to test for unbalanced cells, impedance hotspots, and integrating new monitoring systems that don't require costly proprietary sensors.

Most of this limitation from Ford and GM about their EV drivetrains is because they want control over deployment for monitoring, and so they can cover their asses legally if something like a manufacturing defect becomes widespread.