Well, 9/6/9 isn't really considered thin wall. I guess I'd call that "standard thickness" tubing in traditional diameters. It'll dent, of course, but is probably more damage resistant than most of the tubing used in modern bicycles today.

Non heat treated 8/5/8 tubing is/was pretty common for general use. I've never heard of any issues with denting, etc. I've even used it in some of my own frames, despite leaning toward the Clydesdale end of the spectrum, and have had no troubles, other than more flex than I really prefer.

7/4/7 is too thin for me and was even when I was racing at 168 pounds, on a 58 cm. frame, so my experience is more limited. When I was coaching track racers a couple of decades ago, several of "my" riders used 7/4/7 frames without problem. My wife, whom I stole from a collegiate racing team when they forgot to pay me, has had a 7/4/7 pursuit frame for 15 years or so and really likes it - and it's still pristine despite extensive travel and four or five moves.

So, FWIW, I think the tubing selection you mention would be ideal for a bike for your weight, in your size, and for your purpose, and I don't think you need to be especially concerned with denting it. Worst "real" case scenario is a top tube dent from crashing, which is primarily cosmetic and could be fixed by filling with silver brazing material - although that would require a repaint, of course.