Bitcoin's monetary model is based upon a bogus application of sound money doctrine, but has no value regulation mechanism in it that tries to make bitcoin keep constant economic value (or slightly and predictably increasing or decreasing value).  In other words, bitcoin has no deflation/inflation control AT ALL, and has fallen into a speculative deflationary spiral.  At the same time, it has suffered HUGE seigniorage.  That's about the worst thing one can have as a "currency".  It is very remote from Nash's "ideal money" that keeps constant economic value, and is hence a risk-less fluidifier of economic transactions, which is what a currency is supposed to be.

It is this SAME sound money doctrine that forces the block rewards to go down, and forces a fee market to emerge, which it only can if transactions are scarce enough so that people pay enough fees to do a lot of PoW by miners.  THIS is the problem that Satoshi didn't solve (and is, as far as I know, not solvable game-theoretically).  There is no way to have a sufficiently lucrative fee market without at the same time having block size limits that make transactions scarce and difficult, but what's worse, there's no known mechanism that can regulate that automatically and is robust against being gamed by the miners, pushing the fees to whatever the market can bear.

Both these aspects make bitcoin into a highly speculative asset that is only good for large transactions where the market can accept huge fees.  But that's reserved for a relatively small set of people, is not going to go mainstream as the world's means of payment, and hence there IS no scaling problem because it won't need to scale to world currency levels of transactions (and, as I said, even if it were, that's not a technical problem if it is a decade or so away ; and even then, it is not a problem because not all users need to run full nodes - only miners and big users like exchanges need to).