When you get it apart run your finger over the fine teeth (grooves) on the inside of the brass, perpendicular to the grooves. They should catch your skin as if you was running them over the sharp edge of razor blades. If they don't catch the skin, or they feel smooth, reflect light off the flattened lands (plateau) then they are garbage.

The brass synchronizer ring works like a cluth to slow, stop and match the speeds of the following componenets (clutch disc(s), input shaft, counter gear, and all three speed gears. That's a lot of mass. It must match the speed of then output shaft, hubs and sliders being driven by the momentum of the remaining driveline.

The clutching teeth pictured do nothing to slow and match the speed of the rotating masses, they simply line-up the teech for the slider.

Try fine steel whool to polish the cone surface of the speed gears. It should polish like glass. Too course and it will shorten the life of the new brass.

The smaller, lighter the clutch disc the easier it will be to shift fast, which has already been stated.