As you mention, never put all your eggs in one basket and you will have a greater profit when investing in less popular (or smaller altcoins). On the other hand, investing in ETH is a much safer bet so it all depends on how much risk you want to take.
Absolutely , there are thousands of cryptocurrencies in existence and there are Hundreds in TOP rank that we can choose so why need to invest in single coin , also there is Bitcoin that is more safer and better so make it as our priority.
I may want to advise buying Ethereum also because that is what major altcoin means to me , and of course Binance though some news it was risky but for long term , I think I am good in this one.
I believe altcoins are not to be held for very long, it's okay as long as you are just holding them until the bull run and then selling them instead of keeping a hold on them thinking that they will become more valuable in the next bull run because that is foolish. Even the most trusted altcoins can face problems on the way to the next bull run, and one can also buy more if they sell them at their best price and then the market drops which always happens after the bull run.
So, the only cryptocurrency that deserves to be held for the long term is Bitcoin, in my opinion, and altcoins are good only for short-term trading where one can get a few percentages in profit and then sell them so that they don't risk losing their investment in case something goes wrong with the projects.
A good portion of your portfolio should be invested in BTC. During a bear market, consider using that time to buy more BTC. However, it's also important to hold some altcoins. What I recommend is to focus primarily on high-quality altcoins that have the potential to significantly increase your portfolio. But remember, it's crucial to take profits along the way to avoid the risk of losing your investment.
Currently, we're in the pre-halving year, and BTC dominance is on the rise. Apart from holding BTC, this period offers an excellent opportunity to invest in altcoins. When BTC dominance eventually reverses, altcoins can make investors millionaires, as they often do.