Actually I was thinking machines like the Creality3D ones (like the Ender 3S, I just bought one recently) which while far from perfect perform miracles at their

Actually I was thinking machines like the Creality3D ones (like the Ender 3S, I just bought one recently) which while far from perfect perform miracles at their (<$200) price point, in large part due to having a stiff frame with few resonances due to being built from commodity T-slot components. Even the Prusa i3 mk3 now uses T-slots for the base, though in their case it seems to be more of a DFM improvement. You're right though that sheet metal is very prevalent in the mid-range 3D printers and is an excellent choice for machines built in volume.