LUNA that you invested has failed, but ETH, ADA and DOT will definitely last until 2026, in fact the price will definitely continue to increase when the bullrun occurs, therefore you don't need to worry about investing in ETH, ADA and DOT, because you will definitely get profit in the long term, but for THETA and AVAX I can't give an opinion, because I only know and invest in ETH, ADA and DOT.
We never know what the future of an altcoin project will end like, if we are too optimistic about the project then it will be a mistake,
take a look at Terra Luna, who would have thought LUNA would end up being a Scam,
of course from this we can learn that we should not expect too long in the crypto currency project.
Before what happened to LUNA followed by FTX, people used to have too much belief in altcoins and even used to keep them for the long term, but as soon as it crashed and caused people millions of dollars in losses, everyone stopped believing in altcoins for the long run, and most of the people now buy and sell altcoins only for a very short period of time only to gain a few percentages of profit because they are still afraid of holding them for long.
Apart from Bitcoin and Ethereum, none of the coins in the whole cryptocurrency market are trustable for being held for the long run, other assets must only be bought and sold for a very short period of time and if they are kept for long, they might make you lose money.