By that logic, the supply of 1996 Toyota Corollas is also limited, in fact even more limited than Bitcoin's. Should we therefore invest in 1996 Toyota Corollas?
Sure, comparing and old physical asset that deprecate over time with a pure digital asset built on a blockchain makes a lot of sense. Currencies are way easier to trade than physical goods.
Everything is a question of supply and demand, it does not mean it's valid to compare every goods to another on the market.
Well, if you have a theory of prices that only applies to one good and fails when applied to any other good, it means your theory is rubbish. This is why we must check whether the proposed theory works when applied to goods other than bitcoin. It's not a comparison. Although, there's nothing wrong with comparing different goods either.
Bitcoin is limited until a sufficient number of stakeholders decide that the number should increase. While it may be true that this will never happen, it isn't bounded by physics or math.
If there is anything to learn from LUNA/UST, it's that the quantity of tokens in circulation has basically no bearing on the the _supply_ of tokens offered for sale at any given price.