I don't know how Polar decides what is climb or ascent either.
I guess the only way I would do it is perhaps what you've already mentioned. I'd insert 2 lap markers at the same point on every file and isolate the info for what would now be "Lap 2". Lap 1 and 3 being the portions that can be affected by traffic, etc. It appears that you have automatic lap markers appearing or a lot of lap markers already so I'd get rid of all those first.
I just ride without worrying about hitting the lap button any longer so when I download the file there is only one lap and I can create lap markers where I should have hit the lap button if I had the discipline and brains. On your route, I'd insert them about mile 2.75 and 6.75 on all your files.
I think you can copy this section to another file, do it again with another ride, and then create a comparison where the graphs will set atop each other.
I haven't played with the reports. What about those?
OK, now I'm going to have to go turn on the home computer and see what it does. I rarely track heart rate so the only comparison I'd have is speed, but you could compare heart rate also. Not sure that this is the time of year when I really want to be looking at these stats. Strong legs but barfo on the heat (like that medical term?).