I guess that would be the case if the battery was 100% lithium. But they are not (and cannot be) If I remember correctly the issue with increasing density in lithium batteries is their propensity to catch fire + explode (due to dendrites forming between lithium plates)

So a better battery tech might have a material that can store less electrons per m3 within the "active" material - but it can contain 30% more.

Really? If that is the limiting factor, then there is a lot of hope, because lithium is a tiny portion of a battery weight and volume, something like 1%. It means we could theoretically improve the batteries to hold say 30% lithium, for a 30x improvement in density!

You have to choose your trade offs.

Aluminium is abundant compared to lithium, and if the charging times are as good as they’re saying it might be worth the loss of capacity.

That's an interesting comment that might explain why we are using lithium instead of some other metal. Do you have a reference that discusses this?

Yet batteries have steadily gotten better even since the introduction of lithium.