A couple of things: first, the canard about "much higher THC content in modern pot" is itself a myth. The THC content has not changed substantially. This myth can be traced to a change in the methodology of the government lab that tracks marijuana potency. Prior to some time in the 1980's, they were prohibited from buying marijuana, and so had to depend on donated samples which, unsurprisingly, tended to be of very low quality. So, they were systematically underestimating the THC content by a huge margin. The law was changed in the 1980's to allow them to buy pot for testing, and the results instantly fell into line with reality. No big deal, right? Well, it wouldn't have been if overzealous high school health teachers and guidance councellors hadn't seized onto the apparent (meaningless) increase in tested THC levels as evidence of "stronger modern pot." Probably the urge to do so stems from the fact that around this same time, many former flower children were reaching middle age and struggling to figure out how to justify telling their children not to smoke pot. So, the "strong modern pot" legend was born, and endures to this day. Meanwhile, most people in the US are still smoking the same low-grade Mexican ditch-weed that has been around since who-knows-when.
As far as actual overdosing goes, a couple of things are worth mentioning: there is a fundamental limit to how high a blood-THC-level you can attain by smoking, but not by eating. This is why people will report different (stronger) effects when eating marijuana/hash than smoking it. So, if it is possible to overdose, you will almost certainly have to do it by eating the drug, and not smoking. Likewise, even if marijuana is stronger than it used to be, the extra THC probably isn't ending up in people's bloodstreams anyway. That said, I've never heard any reports of an actual overdose. It is known to give some people, in some situations, panic attacks, which can be very frightening but are not inherently dangerous. People are also known to faint, although it's unclear if marijuana alone does this, or if it is some combination of that and alcohol and tobacco. The fainting does seem to be physiological, though.
That said, you would expect that, were it possible to OD, we would have heard of someone doing it by now. There are plenty of people that aren't shy about getting as much THC into their systems as possible, as often as possible, and yet they don't seem to be overdosing. So... I'd say "myth."