

Correct. When we hear concerns about a declining population, the concern (typically) isn’t that a population should always be rising, or even that it shouldn’t shrink, it’s more about the long-term economic stability of the age distribution of a population within the demographic pyramid. If your demography skews significantly older, you’re going to have fewer working age people supporting your economy and more post-retirement age people needing to be supported. This can do double damage to government revenue in particular, as they will see a simultaneous decrease in tax income and an increase in pension payouts, and this can lead to a sharp contraction in the available share of the budget for all of the other government priorities.
It’s a bit ironic in this case, as this is pretty common in developed economies, and typically the way you would offset this is via immigration, as that allows you to tailor your requirements to exactly what you need to balance your demography, and so anti-immigration sentiment is only likely to cause a more severe spiral.
SpaceX lifts more raw tonnage into orbit than all other agencies and private organizations combined iirc, and directly controls an ever-increasing proportion of US government space-based assets, to say nothing of Starlink. Tesla, while sales have dropped, has not really seen a corresponding sustained drop in stock price (where most of his corresponding net worth from Tesla is actually located) in the meantime, though we will see if that can be sustained long term (I, for one, hope it falls off a goddamn cliff). As for your other point, Twitter (now X) and Grok by extension are, frankly, not a major factor in his worth, when assessed next to those other factors.