I agree with you, that when we trade, we better hold more than one coin. it is true that there are people who say that trading bitcoin is still more feasible compared to altcoin because of its popularity. and people's views of altcoin which are negative because many coins are junk. but in my opinion not all altcoin is rubbish, I still believe in altcoin which has long been in the crypto market. I myself trade with more than one coin, and the majority of the altcoins that I hold I use for daily trading and I trade long-term with bitcoin. so I think, it is very feasible to trade in cryptocurrency, so that the opportunity to get greater results.

My friend, a former Forex trader, refused to trade Bitcoin in our favor of trading Ethereum.

To my question why, he replied that trading in Ether is much easier, it is more predictable, and with it it is much easier to deal with scalping and day trading.
I prefer bitcoin, because in my opinion, using bitcoin, you can earn much more growth phases for us.

You have to consider that Bitcoin and Ethereum has such huge volumes because they are major trading pairs in almost a exchanges, so someone might decide to trade one shitcoin in an obscure exchange but it would still count in the volume of Bitcoin bacause the person traded it in the bitcoin pair, but when you see the volume of other alts like XLM, you know it's people who specifically traded XLM that the volume is showing so it would be a bad idea to judge by volume, short term trading is good for almost all major alts, not just Bitcoin because their prices are also flunctuating exactly like Bitcoin is.