Oh, I agree with Pat. Stiff mountain boots do not necessarily make the best hiking boots. The old leather Galibier Superguides were the standard for technical ice/mixed/mountaineering boots back in the day but were torture devices when used for hiking. They excelled on the steep stuff but were horrible on the flats. I still have knobs on my heels from those boots.
On my many trips up and down the standard route up Borah, I progressively switched to lighter and lighter foot gear as it improved. I first used my heavy leather mountain boots and then switched to lighter over-the-ankle hiking boots. I wore out three pairs of Asolos in the process. Later, I switched to a low-cut approach shoe and am now in the process of wearing out my fourth pair. Outside of the carry/switch question here's my take on the light weight shoes.
A too thin, flexible sole can lead to stone bruises on your feet and toes. And they don't edge as well as a slightly stiffer sole. This may just be a matter of preference.
I like the "sticky" rubber on most of the approach type shoes. Some people wear them to climb up to 5.9 from what I've read. The only drawback is they can stick so well you might stumble because of the grip.
Approach shoes are expensive because they seem to be this "special" category of mountain shoe.
I don't like Gore-Tex liners in most shoes and boots. They always run "hot" and are worthless if you submerge your foot in a creek or other water source. I had two pairs rot out from the inside because moisture seemed to get stuck under the insole.
Wearing light shoes up and down Borah almost made it feel like my feet were floating compared to heavy boots.
I like a bit of a heel for descents. It seems to be less prone to slipping than a flat type sole.
Some low cut shoes are more prone to ankle rolling.
Clear as mud, eh?