I doubt that El Salvador will be the richest country despite making BTC as their legal tender.
Remember that there are several factors that you must consider on how you define a country's richness. Just because they can potentially acquire tons of BTC does not entirely mean that they will be the richest country. Unfortunately, a country can be rich if they are placed geographically right on the Earth. With their tons of natural resources, they may capitalize this advantage and turn it into richness and money.
While BTC may be the future of currency, this fact alone cannot withstand the other factor that may make a country rich.
Yes and even if the El Salvador have accumulated most of the remaining bitcoin, that won't still make them the richest country in the world. Being dependent on the bitcoin alone won't be enough to at least be a part of the Top 5 richest country in God's green earth, they should have a lot more to offer that will make their country grown in the years to come, which they don't have. Also, 8 years is to short, I reckon it would be at least 2 decades from now to see their improvement.
Your hypothetical is internally contradictory Japinat, in terms of presuming futility involving acquiring most of the remaining bitcoin and also still agreeing that bitcoin has value that might take El Salvador longer to catch up or to surpass other countries in relative wealth.
I don't disagree with your other implied point regarding some kind of need for El Salvador to have something that they produce of value that contributes to their ability to be able to accumulate bitcoin, so of course, it remains a challenge for any country to figure out how they can increase their generation of value so that they might be able to accumulate more bitcoin..
So if we were to get into some kind of fantasy hypothetical and El Salvador were to be able to generate enough surplus income that they could purchase (or mine) all of the new bitcoins, then currently they would be acquiring about 900 bitcoins per day (that is 144 blocks per day x 6.25 BTC per block), but so even if they were to ONLY accumulate 10 bitcoin's per day for the next 8 years - that would be 29,200 bitcoins (10 per day x 365 days x 8 years). Even acquiring 10 BTC per day, it seems that El Salvador would be sitting quite pretty in that kind of a hypothetical in which they ongoingly accumulated small amounts of bitcoin on a regular basis
Maybe in such a hypothetical of accumulating 10 BTC per day, they would not be the richest of countries in the world, but they may have increased their wealth quite a bit relative to other countries who had not been following such a consistently ongoing BTC accumulation strategy...(assuming that they do not lose the bitcoin along the way).
Maybe this is a bit of a fantasy for a country the size of El Salvador to accumulate 10 BTC per day, but the scenario seems to be much more realistic than your opening assertion Japinat that it would even be possible for El Salvador to acquire "most of the remaining" bitcoin... something like that (such an aggressive approach that would accumulate so much of the new BTC supply on an ongoing basis) is just not doable, practical or reasonable based on bitcoin's game theory and incentives, even for countries with the deepest of pockets.