For downsides, i'd like to add that the lack of function overloading and default parameters can be really obnoxious and lead to [stupid ugly garbage].
A funny one i found in the standard library is in time::Duration. Duration::as_nanos() returns a u128, Duration::from_nanos() only accepts a u64. That means you need to explicitly downcast and possibly lose data to make a Duration after any transformations you did.
They cant change from_nanos() to accept u128 instead because that's breaking since type casting upwards has to be explicit too (for some reason). The only solution then is to make a from_nanos_u128() which is both ugly, and leaves the 64 bit variant hanging there like a vestigial limb.
That depends on your definition of correct lmao. Rust explicitly counts utf-8 scalar values, because that's the length of the raw bytes contained in the string. There are many times where that value is more useful than the grapheme count.