Long term investment is not related to Spot, Margin or Derivatives.
When you invest long term, you must keep your coin in your wallet, not on exchange. If you mean Spot, Margin or Derivatives, you must store your coin at exchanges. That is bad in security for your coin and capital.
In addition, if you invest and store your coin at exchange, you can easily to go with trading because it is very convenience to trade on exchanges. Then you will change from long term investment to trading and it is bad.
Actually, long term investment is kinda the term we are just using for the span of time we use to keep our tokens or coins in our wallet. But I think if I will be choosing among them, it could be Spot. I don't know some other things that he said, trading in spot is for all kinds of people whether they are newbie or expert all people uses spot to trade. He can read some info in Binance academy if he want.