Guys, I'm late to this conversation but I just recently test rode a Road Glide ST.. (I currently own a 2020 Challenger dark horse)
I'm also coming from years of owning sportbikes. Got into cruisers when I hit my mid 40s. MSF instructor and have done plenty of track days.
The new 117 engine is a beast. It does seem to have a little more oomph from the line compared to my Challenger. Maybe it's the throttle response (and yes, I have the Dynojet ECU flash, throttles synced, full 2 into 1 exhaust, air intake, etc) Did everything you can do to the Challenger except a LLoydz cam. My bike runs perfectly and I wouldn't change anything on it, or even let the dealer service it for risk of updating something that would negatively impact it.
The ST runs much better than previous versions of SGS or RGS. (and I had three different SGS all with M8 engines, one with stage 2 cams)
I honestly think they did a pretty good job with the ST. It is a stripped down version of the Special. Has same technology including RDRS, NAV, Apple Carplay, etc but no passenger seat or rear pegs. The fit and finish of the HD is hands down better than most bikes on the market, including the Indian. Nothing on it feels cheap. I wish my Challenger felt the same. Before the Challenger came out I was riding my Street Glide Special. Took a look at the Chieftain and hated the "plasticy" feel of it.. Didn't purchase... Came back when the Challenger came out and only purchased it because the handling and performance was better than Harley's. The gap is closing now with the ST. I love my Challenger but with the ST, and excellent fit and finish, extensive aftermarket parts, service, etc. The decision is getting harder. Time will tell. For now, I will continue to love my Challenger.