Hello from texas down between houston and galveston. Bought a new 2018 gsxs 1000 new 5 months ago and love it. Big change from the harleys and cruisers im use to,still own 2 harleys tho but my gsxs is gettin more miles and more love. Probably the most fun that ive had in 2 wheels in a long time.
I too came from 2 previous cruiser and yeah the bike is a riot.
The 2018 throttle on mine is still twitchy yes but I'm getting used to it.
If you haven't already, adjust out all but 1mm of slack from your throttle cables. Makes a big difference. Next is checking that the TPS is measuring correctly. If still too twitchy, sounds like the throttle sleeve from the new Katana has a better geometry ('cam') for coming on throttle from totally closed.