Again I envy you, for having the trails to get out on. Ain't no reason to give up those for the sheer joy of it, the suggestion I made was a way you can focus on the goal - but you don't need to run that way every time you go out! Running wouldn't running without something like what you described.
FWIW, when I was 20, after months out with Achilles problems, I started back running that same 40min I told you about. I was not a very good runner, but between that and pool running (5-6 days a week, 1 session of each several of those days ) I found my running form and fitness returned over a period of 2-3 months, and I was able to do that last week (4x9 tempo/1min jog) at down to sub530 mile pace. And it helped me get under 120 for a half-marathon. Then, when I started running with my uni team over the next couple years, I was able to build up to what I what I felt was my sweet spot of mileage - 6 days a week, total 65-70ish mpw (1 long run + doubles 3-4 days/week with tempos + progressions + intervals) to get me to my best times.
I tried this same thing again in my 30s, the last time I was able to run regularly, after several years of non-running, and it helped again (combined with biking/elliptical) - got me to joggerishly reasonable 10km times(sub 6-min/mile), on lower mileage.
So while I do think this could be a way to get you running faster and build up the pace to run a faster mile, see if it works well for you and how you respond. I hope that others out there can provide other approaches for you to try