FWIW from a driver perspective this isn't really resolved fixed, I'd consider
that a bug. Using GL_UNSIGNED_BYTE indices will never be the optimal solution,
but clearly the driver could do better, as evidenced by the driver for some
other OS (I don't know what the driver does, but it could for instance maintain
a shadow copy, translate indices with a compute shader, the problem likely is
that the driver translates the indices on the cpu for each draw call
currently).