for sure dominance is an important metric to watch, in this current market, it only takes btc dropping a few % and most altcoins will follow, hence, you should only hold a small amount of your portfolio in altcoin, and most in btc, using short positions to cover these small drops
Of course, today the state of the cryptocurrency market is such that investing in all cryptocurrencies is a dangerous and thoughtless action. If you do not take into account the highest-rated cryptocurrencies, especially Bitcoin and Ethereum, then some altcoin may be a profitable investment, but for this you need to pay attention to future prospects and their relevance in society, in addition, a real practical use for such altcoins of these coins for something, such as the Throne or EOS for gambling and how active this use is.