Light-weight wrapper over C, so as fast as C when you want it to be. Message passing isn't as fast as, say, vtables, but is still quite snappy and flexible for loosely binding objects together. No generics avoids code bloat.

In practice obj-c apps were snappy, e.g., good perf on extremely limited hardware of original iPhone. SwiftUI (I assume) of MacOS settings app much slower than the old version it replaced -- too much heavy programmer framework magic resulting in slower final code? That's my diagnosis/guess from afar (I might be wrong ofc), a pitfall that objc did not tend to lead developers into.