I have no idea how eccentric muscle contraction affects the look of the exterior body. So I am unable to respond to that. Sorry. Someone else will have to respond on that front.
We have a slightly different view on mobility. It is not random flexibility that results in “more energy/blood flow, release of toxins, better mood, and overall better health”. If that were the case every contortionist on the planet would be healthy as a horse.
In yoga we work to mobilize some things while stabilizing others. In fact, I’ll take it one step further. It is the overly mobile student who is at greater risk in yoga than the stiff one. The overly mobile student has little action in their body (as a result of hyper mobility) and has a significantly increased risk of connective tissue damage especially in the joints.
Even with this set aside, opening the body with care, progressively, over time, is much healthier than doing it in a week. It cannot be forced even with the lure of the benefits mentioned. When it takes a human being 20 years to create an imbalance in their physical body it is simply inappropriate to “fix” it in a month. It is too much too fast and leads to serious ramifications more times than not.