My theory, twins are narrower and feel "just so" when getting thru a set of bends. Also helps that you can surf the wide power band allowing you to concentrate on the corner rather than shifting and all.
Most twins have a heavier crank but the weight is distributed low and in front, giving an added feeling of stability and carvability while leaned in.
Alot of buzzy fours with the weight higher and lighter reciprocating assembly (crank, rods) spinning faster can feel flighty and nervous.
Oh and upgrades ? I have been known to want to upgrade my budget rides immediately (myself) but I have never bought a premium ride like a front line supersport and felt the need to do anything other than ride it