In my experience not being able to use iterators is rare in most Rust code. Inner loops that have array lookups are overwhelmingly iterating over collections. It's much more common to have to drop down to unsafe code because you need to implement some low-level data structure that Rust's ownership rules can't yet prove safe.

I have personally never seen the bounds checks be a problem except in microbenchmark-like things, and those are almost always compiler bugs involving missed optimizations that the compiler could have done but does not presently. I think "the design of Rust does not guarantee the possibility of matching C++ performance unless you use unsafe code" is too strong a statement.