I agree 100%. I also think only investing in bitcoin or investing in one of the altcoins is not a smart strategy at all. You need to keep a holistic view and invest in btc and altcoins that show promise. You cannot be dismissive toward alts. A diverse portfolio is key for maximum gains in the short and long run.
Undoubtedly, diversification is the best way to go because we always hear people say that we shouldn't put all our eggs in one basket, and if we ignore that saying, it means we are being deliberately ignorant which isn't a good thing, I believe.
So even though we know that Bitcoin is the best cryptocurrency in the market and that it is the most trusted one when it comes to making investments, that doesn't mean we don't have any worthy altcoins in the market to add to our portfolios.
We should do enough research and find out the best altcoins in the market and then make investments in them alongside Bitcoin to have higher potentials for profit when the market starts going up.