If you have a wasm application with vulnerabilities (e.g. in the libraries) there are no mitigations that native binaries provide, so simple buffer overflows give you RCEs again. It's still within the sandbox, but the threat is as severe as running eval on user supplied inputs as there might be useful stuff in that sandbox.
That aside, if the C-to-wasm compiler were to add some of the safeguards mentioned it does sound like it'd go some way towards lessening the potential impact.
The practical difference is that it's a lot harder to assure code written in unsafe languages is free of defects like this since they manifest as benign operations (every write to a buffer is a potential vector) rather than obviously dangerous operations. Concretely, you could grep for eval and convince yourself that each use is OK (assuming it's rare - it ought to be) but you couldn't do that for common language constructs that could be exploitable like writes to arrays/pointers.