My brother in Christ, have you heard about our lord and saviour the Scientific Method and the proliferation of cross-domain ideas? How do you imagine the li-ion batteries came about as the go-to energy storage solution? Incremental improvements of ideas would be my guess, ideas have to start somewhere and of course they’re going to be hyperbolic since researchers are both excited and have to draw attention to their ideas.
I sympathise with your point but the alternative is little to no research into different battery technologies because close to nothing will ever emerge as a competitive day-one drop-in replacement, but some ideas may prove exciting to others who understand the value and they might push the ball further towards realistic alternatives.
Not my area of expertise but density is the wrong concept to be looking into remaining equal, its pressure. The amount of helium gas you pump in to the balloon creates a certain outward pressure that’s at equilibrium with outside air pressure, that’s why it doesn’t collapse (if you were to place the balloon in a vacuum then it would expand and probably burst, that’s usually what happens when a child loses one and it escapes higher up in the atmosphere to lower pressures)
The atmospheric pressure simply isn’t strong enough to overcome the outward pressure.
Bonus point: density is actually the reason why a helium balloon floats, its less dense than air so it wants to float up. Much like a rubber duck or ice cube in water.