I just spent half an hour in a Podiatrist's office to learn about shoes, footcare, and hiking.
I asked him his take on the traditional contention that tall heavy boots provide needed support and prevent injury.
His answer: it used to be true, but the strength of modern running shoes now negates the need for boots. He said that shoes are built stronger and can provide the needed support in the sole — thus reducing the torquing of the foot that used to necessitate hightop boots. (I am paraphrasing heavily here.)
He'd never heard of lightweight backpacking but he said that backpacking in trail runners is perfectly reasonable when modern shoes are used.
One more tidbit: he said he dislikes all "gear company" shoes. Buy "shoe company" shoes, he said. And this guy was a shoe geek if ever there was such a thing. He knew all the models and their strengths, weaknesses, and relative dimensions. I brought in some Nikes from 2001 to show him the shoes that gave me the least knee pain for some reason, and he knew their model name and year.
If you're in the Lower Mainland, I recommend Dr. Roy Mathews in New West.

