On the point of chain stretch, they don’t chains wear. The load reequired to stretch a chain is way beyond what your legs can provide. On my converted bikes I change the chain at 0.75% wear which is what you should do anyway regarless of what drivetrain you use. If you do this then chain wear will not become an issue. I get a few hundred miles (no odo so I cannot tell exactly) before slack becomes an issue, I have found that is when the chain reaches 0.75% wear funnily enough. Change it at 0.75% wear and you will not have a problem on a tensioner less setup. Using a rensioner may allow to run the chain for longer but this leads to it own potential problems.
I have tried tensioners such as BB mounted one like the black spire picturted above and hanger mounted ones and with all I found chain wear caused issues with these too. The BB mounted one needed adjustment regularly which was a pain and the hanger mounted ones never worked well in muddy conditions. Tensioners work but they are not the only solution.
Oh with my tensioner less solution I have never had a chain jump of so it must a good solution.