I won’t bore you with detail but I’ve done a lot of turntable, plinth, armboard experimentation, theorising and building. In theory, perhaps, no seperated armboard is the best solution. However, I have found that a unified armboard and chassis combo works just as well and has many practical benefits. What I would also add is that the material and form/construction of said armboard can have a profound effect on the performance of the attached arm and I personally spend a great deal of time designing the armboards I use (I wouldn’t personally use just two screws to mount an armboard).