I wonder why it's working for some people...
It's working for ALL people! Not ALL stutters on landing are caused by GSX! On MSFS forum, we read reports of users who didn't had GSX, with somebody even using an XBOX, so clearly he couldn't have had any access to GSX.
GSX 3.5.9 fixed only the case where the stutters on landing were caused by the Livery Manager which disabled the GSX replacement tug for the default Asobo pushback tug: its absence cause that stutter on landing, we could only fix this specific case, because this was the one caused by GSX (or more precisely, the Livery Manager).
If you spawn at a gate without calling GSX, and you see the Pushback tug (it's a GSX model, but it acts as a replacement for default one, so it works from the ATC menu), your GSX is all fine and your touchdown stutters are caused by something else.