Most of the altcoins are indeed very volatile, and risky to hold in the long term, only a few altcoins may be safe for long term investment. it would actually be easier to invest than to trade, let alone bitcoin. for those who are already proficient at trading, of course there is no obstacle to doing both, but for many speculators who are looking for new altcoins to invest in, until the price soars and sells them
All altcoins are very volatile, except stablecoins.
So, basically, all altcoins are high-risk to hold for a long time. No altcoins are really safe to hold long-term, including the top altcoins. Any altcoins can lose their values significantly at any time and maybe never hit again their ATH. I have experienced holding some altcoins that the prices never return to the ATH.
By the way, invest and trade are almost the same, it is only easy if we know it well. So, not sure if investing is easier than trading. It depends on the knowledge of the individual. Regarding investing all in Bitcoin, it is not a bad idea but I assume most people prefer to diversify their crypto assets. People want to optimize the chance for bigger profits.