Nothing wrong with 19" wheels - ask any GS rider. They handle better over shitty road surfaces and tbh I never noticed any worse handling on perfect road surfaces either. I'd go so far to say that the GS is the best handling road bike ever built.
Cas
Which GS, exactly? Surely not the R80 G/S or R1200GS ? Those aren't road bikes... And I had the misfortune to rent a near-new 2006 R1200GS in Australia for a planned 8000km trip. Most unreliable bike I've ever ridden, and ended up having to be towed back to the dealer mid-trip. Quite mediocre handling. The F650GS-Dakar we rented with it was better in every respect.
As far as I am concerned, my 2009 BMW F650GS twin handles better than my R1200RS, especially on bumpy back roads. And a lot better than my Zero S with its top-heavy Power Tank and too firm suspension.
This was a honeymoon, wife & myself + full camping gear on two bikes. Western Australia only has (or had, at the time) one BMW dealership, in Perth.(*)
we left the bike 1000km away at a campground, to be towed, but now had to make our way back to Perth 2-up on the F650 to get a replacement bike.
This was the original liquid-cooled Rotax-single 650, which BMW called "Funduro", not the later twin; the F650 was already well-used when we got it, with ~46K km and 2 y.o., but managed this beautifully, carrying 2 + 40kg of luggage, and still managed to return 23 km/l at 120 km/h (54 mpg at 75mph). And that with low, dirt-oriented gearing and a 19" front wheel. It also managed fine with aux loads on the battery connected directly (battery chargers, communicators etc.), whereas on the R1200 they worked at best half the time.
(*) The next closest dealership was 2700km away, in Adelaide, across the Nullarbor Plain .