In this market one of the most popular strategies when the market is going down is to buy the dip and while this can be incredibly risky with many altcoins the risk is a lot smaller if you decide to invest in bitcoin.
It is true that if you invest now and the bear market happens then you could be losing money for months or even years but for a long term investor that is not really a problem especially when we know that bitcoin has an incredibly high chance of surpassing its previous all time high.
Your statement seems true. However the % risk is the same, regardless of the amount of money you invest.
The work needed to examine in detail all the details for a project is the same, regardless of the amount of money you invest.
So if you invest in BTC, you can easily earn some 5-10 % return in a month (after some day trading)
But if you invest same amount of $ in small alts, you will have to wait for years, hoping that their project succeeds.
So 5-10% in a month or uncertain % in uncertain number of years?
At the end of the day this is your decision, since bitcoin is so big compared to the rest of the coins in the market it is obvious that you are never going to get profits as big as whatever you can get with altcoins but your profits are a lot more predictable.
When it comes to altcoins you do not really have a way to know how much money you're going to get out of your investment, if you get any, but if you are not risking a lot of money it could be worth to try your luck with altcoins because if you invest in the right project the profits can be massive.