Just because Rust can't easily do things that C can doesn't make it a bad language, but it does mean that, shockingly, there are somethings that Rust isn't as well positioned for as other languages are.
Similarly, there are things that C is bad at. Both at the high level and the low level. At the low level it hides too much of the CPU's features so for some very low level programming you need to drop to assembly. At the high level it has obvious deficiencies, many of which Rust addresses, but for interfacing with the actual hardware it is tough to beat C in terms of convenience.
Undefined behavior and the lack of namespacing don't fall into this category, though. C would be a better language all around if it required that null pointer dereference trap to an error handler (at least on hardware with an MMU or MPU). It would also be a better language if it had a module system.
Not every engineering decision is a tradeoff. Sometimes certain decisions are just better all around. I think that modules and error handlers fall into this category.
Scratch the "not". For example, if I have a small-enough code-base, a module-system, is not worth it, unless it has zero cost. Or if the module system doesn't fit my needs, it will often be easier to create what I need if I don't have to work around what is there. Same with error handlers.
Every engineering decision is a tradeoff, though you may be in a space where the tradeoffs obviously point in one direction.
> All you need to do is take the address of the GPIO register then toggle the bit.
Yes, and that is unsafe. Rust makes you put that in an unsafe block, to encourage you to build safe interfaces. This is a good thing.
> No name mangling.
The alternative to name mangling is not having a module system, with all the fun name conflict issues that come with it. Rust made the right decision here.
> No error handlers to override.
C has no concept of a panic handler because what would be panics in C are undefined behavior. Undefined behavior is bad for safety and understandability of the code. Having to declare an error handler is a small price to pay.
> It does seem odd to me that so many of what would be compiler options in C are hard coded.
Because Rust is safe by default. That's one of its most important features. Being more like C in the ways you mention would mean compromising that principle.