I'm not Matt, but I do wear waterproof footwear ten months of the year, or more. Depending on terrain.
Roger asked: "What will the GTX liner achieve?" It will keep feet dry, warm, and unmacerated. "If you walk through a creek the water will come in through the big hole at the top." Not if you wear something else, or nothing, to cross the creek. "If you are walking through wet grass, your socks will get wet." Not if you wear gaiters, or high cut boots with low socks. "If it is raining, the water will run down your trousers into your socks." Not if you wear rain pants or chaps that come over the tops of your gaiters or boots.
"But so what? Wet feet won't hurt you: we walk through rivers all the time. The mesh lets the water drain out quickly; GTX would keep your feet very wet."
This, I respectfully offer, is not necessarily true in environments unlike Roger's. In waterlogged moss, squelchy bog and grassy marshes, water will certainly not drain out. 'Quick dry' mesh shoes will not be drying, ever. This leads to a day spent with macerated feet, never mind the silt and mud entering through the mesh to chafe the softened skin. Even without considering the temperature, none of this is comfortable in the long term. Should the resulting cracks and blisters end up infected (bog and marshwater, remember) it could be worse than uncomfortable.
"Sorry, but the idea of 'a shoe with a mostly mesh upper, that is waterproof' is just not realistic imho. All the GTX liner will do is give you 'prune feet' in hot weather."
Maybe my feet just don't sweat much? Maybe my wool socks mitigate the pruning? All I know is I can be guaranteed pruned feet WITHOUT the waterproof footwear. Because of the environment I walk in. If I was walking dry trails with occasional water crossings followed by more dry trail, different story.
OP, btw, I have enjoyed the Keen Gypsum Mids, which I think are pretty light for a higher-cut boot. The sole is quite flexible, with good traction. The membrane has never wet through, and there is a fairly substantial amount of mesh compared to some other Keens. In fact, they actually do 'breathe', circumstances permitting, and I finish even a 20+ Celsius day with socks no more than slightly damp from sweat.