The root of the issue actually appears to be that OpenBSD still supports extremely old and slow architectures (that struggle to build itself):

  alpha 
  amd64 
  arm64 
  armv7 
  hppa 
  i386 
  landisk 
  loongson
  luna88k 
  macppc 
  octeon 
  powerpc64 
  riscv64 
  sparc64 

For a project with such limited resources as OpenBSD, it seems wise for them to drop support for a large number of these legacy platforms and focus on more widely used architectures.

I understand that, supporting more architectures actually help uncover more bugs. But you could still do that with a supported platform list that is 1/2 that size.

https://www.openbsd.org/plat.html

Look at what DragonflyBSD has been able to accomplish, truly competitive with Linux regarding performance and features, with the smallest development team out of all the BSDs.

They can do this in large part because they focus on only 1 platform (supporting arch64).