First off, arguing over which crypto is better than another usually is pointless. (You'll see enough of that here) Don't get caught in that. As long as you explained your point backed by facts, who cares what the other person thinks. Everyone is entitled to their opinion and beliefs. You'll learn that not everyone will agree with you even though you may have sound facts. I know it's infuriating, but its like that at times. Point of this is some things aren't worth arguing over, and crypto is one of things.
Yup! you are right I personally think that bitcoin is the best of all coins, but there is a good profit in engaging with other Altcoins if you can see their worth I think there would be no trading with other Cryptos if there are no Altcoins that is the fact and I think there is a need for altcoins to exist in engaging other terms of earning with bitcoin and there will be other investment for people that wants cheap investment they can surely invest and choose what is the best Coins for them.