First of all, you're usually throwing two (and definitely if you have the feat or Fast Hands).
You're throwing one, unless there's a house rule to mitigate that (or you have a feat or class feature). House rules can provide good solutions to systemic problems, but that doesn't mean the problem doesn't exist.
Second, it's definitely not a trivial amount of damage as it's almost the same amount of damage you'd deal in melee since you still add your strength to the damage roll as normal (it's the same as a short sword or scimitar - except thrown).
Nobody goes into melee with a short sword and nothing to back that up. Everyone who would want to use a short sword will also have some sort of ability which increases that damage. And since you can't use Extra Attack (unlike, for example, an archer who is forced into melee), that means you're dealing less than half as much damage as anyone else.
The big issue is the combination of one attack with Disadvantage on the attack roll. If you could make two attacks, and had a reasonable chance of hitting with those, then you'd be dealing enough damage that it might actually matter. That's where the Dex-based fighter stands, even if they're specialized in melee.
Third, so now this is only applicable in your mind to boss battles, and only if that boss battle is always beyond 30'?
We're talking about the very specific situation mentioned in this thread, which is a boss battle against a boss monster that can stay at range. It might seem like a corner-case scenario, but that's what dragons are, so it's definitely worth considering.
In most other situations, the barbarian will be fine. Either it isn't a boss monster, so a javelin is still meaningful, or there will be some way to close the distance.
This is becoming silly. I wish you'd articulate your objection in a more straight manner than the whack-a-mole style of argumentation you're adopting here. Is it that you want them to do as much damage as they'd do in melee? What is your objection aside from the canard of "playing mario cart instead"? Let's have it straight, without the exagerations.
The disparity in efficacy between a specialist and a non-specialist is too great, and it gets worse as you gain levels. It's a systemic issue with Bounded Accuracy, that every relevant aspect of an enemy will always improve across levels, while only specific aspects of PCs will improve. At higher levels, the game is balanced for specialists to operate within their areas of specialization, and trying to operate outside of that zone is an exercise in futility.
As a secondary issue, Dex-based melee fighters have a much broader area of specialization than Strength-based melee fighters. They can stray further from their wheelhouse, before experiencing that drop-off. It's bad game design when players are sidelined for long periods of time, but when some character concepts are sidelined more frequently than others, then it's also un-fair. (See also: The Problem with Deckers.)