I'm in the third group, as described in this article:
One interesting thing is that some elite athletes have a more limited range of motion in their legs than others, but it's claimed that this leads to more efficient form and motion!
My strategy now, for dealing with my very tight leg muscles, is to just make sure I'm active relatively frequently, but I have no intentions of doing much strenuous activity. I don't think distance running or anything else hard on the body is worthwhile for me (or anyone else) unless it brings joy.
(Side note: There's lots of evidence that cardio burns virtually no fat (very insignificant amounts). Please don't think you need to be tearing yourself up to maintain your figure. Focus on your diet for your figure and exercise/activities for stress relief and pleasure.
Some say tight leg muscles is at least in part neurological. I've heard that when someone is "put under" for surgery they are totally flexible. There are some folks that claim to have strategies to address tight muscles more from this perspective.
This guy has an interesting theory about tight hamstrings:
Upshot is, as with most everything else, don't believe everything you hear and read. Lots of conventional wisdom is outdated, unproven, or at best over-simplified. In this particular case, unless something extreme is going on, I hope people aren't getting surgery for tight muscles or trying so hard to stretch that they get injured. If it doesn't feel right, question it!