I dont disagree they can be done right but the extra effort isnt straight forward.Done properly and bike bodies are very good, quality of manufacture etc is typically high and they stay in balance well. However.... It's crucial to have them hard mounted to a manifold and not via silicone. Otherwise the balance will drift without question.
Suggest researching on Sandy Brown's bike bodies setups he does for the TU and XU engines. Sandy for a long time was using Keihin bike bodies over Jenveys even on money no object race builds.