I doubt the value of both GT liners and leather boots themselves for hiking/backpacking.
In the first place, even nominally "waterproof" leather boots will take in water if the water is over 15 cm deep. So dry-footed stream hopping must be restricted to very shallow streams. And leather boot users can confirm that leather boots, once wet, take an inordinately long time to dry out.
Second, leather boots often have thicker soles, thereby elevating the foot above the ground, increasing lateral torque on the foot and the likelihood of a twisted ankle in rough terrain. And leather boots reduce nimbleness, since they don't allow for the the foot to feel terrain and adapt to rough ground.
Third, it's my suspicion that leather boots are harder to fit than off the shelf runners and therefore create more blisters. But I wonder if this is anyone else's experience?
Fourth, I'm deeply suspicious of the oft-heard mantra that boots offer more ankle support. If the boots are higher than the ankle and rigid - like a downhill ski boot - I suspect this could be true. But such a boot would be very uncomfortable to hike in. Hiking boots that barely reach the ankle and are flexible seem to me to offer very little protection. But I'll defer to expert research on this question.
Fifth, the overwhelming consensus of long-distance thru-hikers (especially in the US) is that runners are far superior to boots. Many thru-hikers start long trails with boots, and quickly switch to runners (and much lighter packs). A subjective reaction to be sure, but it's unclear to me why this successful strategy on for tackling 2000+km trails won't work on the shorter trails that most of us do most of the time.
Sixth, there seems to be some truth to the adage that a pound on the feet equals five on the back. This blog summarizes the research.
Obviously, a tired hiker is more susceptible to stumbling on the trail and to injury.
I don't, of course, anticipate that these considerations will alter anyone's allegiance to leather boots.
DISCLAIMER: My background is 30 years of mountaineering including climbing trips to Peru, Alaska, Mexico's volcanoes, Rainier, Whitney, and the Yukon. I'm on my fifth pair of mountain boots (3 prs. plastic, 1 leather, 1 synthetic). So I'm firmly convinced of the value of solid mountain boots on steep, technical ground, especially when it's cold, icy, and/or snowy. But I'm not sure this approach is relevant to hiking. On approach hikes burdened with a pack filled with heavy mountaineering gear and on trails steeper and more rugged than the typical backpacking trail, I tried to use runners wherever possible.
Since returning to backpacking, I've hiked exclusively in trail running shoes. I cover 25-35 km/day with an overnight pack. My shoes weigh 210 g each, offer adequate protection from rocks, and are decidedly non-waterproof. But they are comfortable, light, and dry very quickly.
Of course, YMMV.