Internal thermal regulation is the next best thing for that fool-proof light and usually the component cost to incorporate that is at most a couple dollars per unit, if not cents, however its putting it there in the first place that is the problem. And why is that so difficult? It takes a small but decent amount of effort to put this into the design (and a bit of space)… Technicalities aside, it all comes down to price, consumer demand, and overall mindset.
Many of the modern lights that your paying upwards of $50, 100, 300 for, do come with such features, and in some instances even have battery voltage readouts, and even let you choose how the torch brightness goes down as the battery runs flat (fully regulated, to stepped decrease, to smooth gradual decrease). I even own a couple of these, and they even advertise the ability to run full bore till the battery dies in warm climates!
But its all down to cost. If your willing to pay for it, it can be done. Lets go to the other end of the scale where your bargain bin torch produced by a factory (most likely in china) will have some budget emitter, slapped on a standard led board, and if your lucky thats screwed onto a standard aluminium head/body, in goes a driver (floating around), and in goes a battery. Give it lots of amps, out come some lumens, whack on a nice big lumen figure and away we go.
It might not even work half the time after a month of trying it out, and your asking for thermal design Most of these have the classic LED star mounted onto a tube, so the back of the LED isnt even on anything substantial. They feel cold outside because the heat never even gets out to the tube, your just roasting an LED. But you might have only paid $15 for it.
Again, expectations must reflect what your asking for. Impossibly compact, Impossibly bright, with runtime to boot and most importantly, bottom dollar. As many have stated in the past, you can only choose a few of the above, and rarely do you get to play with all of them. Its dependent on where your goal posts are. A couple years back, and we were WOWing at the short of 100 lumens we could get with a maglight 4D LED! (and its thermal design is pretty poor, it already needs to ramp down after a few mins of 100 lumens!)
So if you want it all, paying for it in some way or other helps you to achieve the goals.
Oh and 5 minutes, 5:32.12315… it doesnt matter. Unless you have gear to internally measure temperatures, there is no real limit to time. It depends on everything, External temperature, air velocity, air direction, air density, types of material in contact, how fast the blood is flowing in your hand if holding the torch, what battery your using, the internal resistance of your battery, the position of the moon (affecting the tide, therefore affecting whether your indoors or outdoors catching crabs in the river), the total thermal design mechanically and electrically are most important.
LEDs dont die instantly past a certain temperature, its accumulated reduction in performance. So how you want to use it dictates how long you will get to enjoy higher performance from your torch. No one says you should stop using it after it passes hand searing temperatures. A better design will let you run it longer and brighter, simple as that.