The actual Light Emitting Diodes loose brighness over time due to, amongst other things, dopant migration which is something that gets accelerated by higher temperatures (though even when disconnected and in storage, it still happens).
(I have some red LEDs which are almost 4 decades old from back when I played with Electronics as a kid and they’re way less bright - barelly lighting up - than the ones I got a few years ago)
That said, the cheap conversion/regulation circuits in those lamps can exposed the LEDs to frequent spikes of voltage or current beyond their spec, and even though most electronic components can handled occasional slightly out of spec power (they tend to be designed with chunky margins), do it too often and they’ll will probably die.
And then, of course, as your college lecturer pointed out, those conversion/regulation when done with cheap designs and components tend to die way more easilly than the LEDs themselves.