Take note that i do not keep any altcoins in my portfolio. There is no strategy that has proven to be successful in predicting altcoins, how can you trust some developers, when a lot of them have turned out to be scammers in the past, and if you are investing because an influencer recommends the coin, then that is a crazy thing to do. I agree with the point that you can get lucky with a few altcoins if you buy a lot of them, but what if you don't get lucky.
That is like saying you wouldn't eat food again because you got sick by eating a specific food sometime in the past. Just because some projects and cryptocurrencies turn out to be bad or scams, it doesn't mean they are all bad, besides, one shouldn't make investments while having their eyes closed. You can't trust anything with a blindfold on, of course, but if you do your research, and evaluate the whole market, I'm sure you will find some useful altcoins as well.
If you don't like them, it's your choice and I respect that, and I agree that Bitcoin is the best cryptocurrency out there, but I prefer diversification and I know that there are cryptocurrencies apart from Bitcoin that deserve some investments as well because they have been around for a long time and have never disappointed their investors.