I traded my 120K-mile GL18 for my FJR.
I'm shorter, 5-9, so that will alter a couple of perspectives.
I no longer needed to carry a passenger, since the Missus got her own bikes, so the Wing became sort of superfluous. My other bike was a GPZ1100 with Givis and covered my solo work fine.
Getting old, and tired of shoving around 900 pounds, even though the Wing's design brilliantly disguises most of it, I wanted to downsize.
The Wing's performance is very good. The FJR's exceeds it by a large margin in every way except carrying a passenger. The FJR can do it; the Wing was built from the ground up to do it.
While indeed the FJR is no supersport, don't tell the guys here who ride theirs in that manner; they won't listen anyway. It will do very, very well when shown a mountain road.
The motor on the FJR is outstanding. I would hazard many if not most FJR riders would call it the best thing about the bike. It will do many things extremely well, including accelerate at near-eyeball-flattening rates.
The ergos are well-suited to taller riders. For me, the two main ergonomic issues were the width between the knees making it relatively "tall" for my shorter legs, getting to be more of a problem with age.
The other is the handlebars are too far forward for many of us, at least for longer rides. The stockers are fine for shorter, more intense blasts, but to cover more bases, risers or replacement top triple clamps or other adaptations are fairly common. Additionally, since I see a fair amount of traffic in these parts, I also extended my stock bars 2" each side, a total of 4", for more leverage during lower-speed work. It helps a lot and doesn't really have any negative effect that I can tell at more rambunctious speeds.
The windshield is unliked by many. I installed a Rifle.com one on mine and it's a vast improvement.
The GL18 is an extraordinary, and incredibly competent, motorcycle. It borders on the unbelievable, how it can do so many different things so well. The quality is beyond reproach. It can tow your Jet-Ski down Lake Shore Drive (I saw a guy doing that!).
But I would not go back, not at this point. The FJR is 200 pounds lighter and goes right well. The weather protection is sufficient, especially with a screen change. My thousand-mile days are in the past, so the comfort is fine.
Hope that helps.
2004 V-Strom 650
2020 Ninja 400 in the hands of the Missus
2004 Suzuki SV650S, also Hers
2008 BMW F800ST, mixed.
In the avatar: 1966 Velocette Venom Thruxton and 1967 BSA Royal Star.