I myself do not think too much about whether the coin I bought must be included in 100 CMC, because in my opinion it does not guarantee us in getting a profit, I prefer to buy coins which I think are good in terms of projects and usability
There is no harm in buying coins ranked below 100 in the coinmarketcap. when you need the coin, and have a clear team and prospect, I think it's quite reasonable to buy it. however, if you invest, maybe 100 coins and above are good enough.