I think you're equating light twins and their certification requirements as if they should be the same as transport category a/c.
That's not appropriate. Light twins have never had to demonstrate that level of redundancy.
In terms of redundancy they should be considered to be a single engine a/c but one where the pistons on the 'single engine' are separated, protecting one 'bank' of cylinders from a problem that has affected the other 'bank'.
If you like, think of it as a way of ensuring an engine failure will only be a partial failure. One that still leaves you with some amount of power available, along with services such as hydraulics, electricity, pneumatics etc.
You may have sufficient power to continue flight. Or you may not, depending on WAT, configuration & handling skill.
Just like a real single.