[greglepore]

Just 2 points-most single chainring bikes with a rear derailleur run what's called a "narrow wide" chainring (alternating narrow and wide teeth) to ensure chain retention. Also, gravel and mountain bikes have a rear derailleur with a "clutch" in the cage spring to prevent the chain from bouncing and coming off. A bike set up like yours without these will have issues on rough surfaces, particularly with a worn chain.

Second, and just a personal pet peeve, chains don't "stretch". They're friggen steel. What does happen is that the rollers wear at the pin-roller interface, which effectively makes the distance between rollers get larger under load (because the hole in the roller is worn larger). This makes the chain more prone to skipping etc. Also, riding with a worn chain eventually wears the teeth on the cogs and chainring into a shape the conforms to the worn chain, making them unusable with a new chain as everything is out of tolerance.