No, it does not have "a bunch of performance issues". It has carefully considered performance vs. security compromises which are largely configurable. GrapheneOS uses hardened_malloc in a very security-oriented configuration and has the option to disable it per-app if there's ever a compatibility or performance issue. GrapheneOS could also offer another toggle for setting it to a performance mode where it isn't significantly slower than Scudo either via dynamic configuration or a 2nd build of hardened_malloc with a lighter configuration. Most overhead is from slab allocation quarantines which are optional.