If you like Objective-C but not Apple's runtime, you should check out ObjFW: https://webkeks.org/objfw/
Actually, I don't get all this "Messaging is slow". In the ObjFW runtime, it's just 12 instructions for x86_64. That's barely noticable. I even used ObjC in an HPC application and compared it to the C version, just for fun. There was no measurable difference in performance.
What's more important in the average application is that the foundation classes are fast. For example, C#'s and Cocoa's dictionaries are really slow (but I don't know why). While C# and Cocoa both need 1.2 sec to insert 1 Mio objects into a dictionary and retrieve them, ObjFW only needs 0.3.