I think 100 coins in investments are relatively safe compared to other altcoins. But we cannot deny their risk .You need to analyze the coin in which you want to invest.
Yes, of course investing in the marketcap's top 100 coins is safer than the ones below it. However, to be safer and further reduce the risk of loss I think it's better to invest in coins that sit in the top 20 or 10 marketcaps.