El Salvador made the mistake of thinking that bitcoin could save their economy and they got too dependent on it, but I don't think they made any mistakes with their bitcoin investment strategy.
If I remember correctly they are holding over 6k2BTC worth over $700 million and the capital they have spent is $300 million. That means the profit they made was around $400 million and that's not a bad profit.
In my opinion, for countries, organizations and companies, those with large capital and can invest long term. They can and should invest whenever they are ready, they don't have to wait for a bear season or a bitcoin price crash to buy, and El Salvador and MSTR are doing quite well with that strategy. The bear season waiting strategy is more suitable for small investors.
I have been active in the thread about El Salvador making Bitcoin a legal tender and I don't think the country bought Bitcoin because they wanted it to save their economy maybe from collapse. They just had a comprehensive plan that includes a bitcoin city which comprises several projects like mining facilities, hotels, resorts, etc. Sadly, the country couldn't go ahead with these projects, but they kept buying Bitcoin. El Salvador’s Bitcoin investment has been profitable, and it seems they have a long-term approach.