There is no absolute "need" to diversify either, especially when someone is early in his/her investment and while still in the relatively early stages of building an investment portfolio.. So if someone is new to investing, and can only invest a few thousand per year, it may well be o.k. to just balance in cash and bitcoin.. and to formulate various simple accumulation strategies... after a few years, the investment portfolio may well end up growing to $20k and then to $40k, and then at some point (upon your own choosing), there might be some benefits to diversifying into some other assets .. but even then, diversification might not be necessary, so each person will need to consider how much diversification is comfortable...
As far as shitcoins are concern, I find all of them quite problematic, and sure there might be some ways to get in and out of them, yet many times there may be too many distractions from the main investments.. so individuals have to measure if they might consider 5% to 10% or some reasonable and prudent amount and maybe they feel some desire (or reason) to learn about other matters, and consider their investments of time, money and energies to help channel their learning.. which might be o.k. if it is down in moderation and does not end up devolving into some BIG distraction that ends up causing loss of focus and even loss of time and loss of some if not all of the power of compounding.. which is something that comes from investing a long time, rather than bouncing around.
Understanding that diversification is not necessary does not come immediately, and as very often happens, we learn from our mistakes. Now when I can draw conclusions from my first unsuccessful investments, I will say that it is difficult for me to call shitcoins an investment, I mean that it is dangerous to buy shitcoins for a long-term investment, since this will most likely lead to a loss of funds. They may in some cases be suitable for short-term trading, but this is not an investment, this is a different kind of activity, and it requires a lot of time and knowledge.
If we are talking about investing several thousand dollars a year in bitcoin, then there really is no point in being distracted by shitcoin, because even 10% will only be a few hundred and we will probably spend more time looking for a shitcoin than it will bring profit. It is better to focus completely on bitcoin, and spend your free time looking for additional sources of income that can be additionally channeled for investing in bitcoin. I have never been very successful in trading, but I always find opportunities for additional income, this is the best option for me.
When you have precisely decided on your strategy, you know for sure that you will only invest in bitcoin, you will not be distracted by shitcoins or trading, then you get free time that you can use more rationally. The order in the investment portfolio and the order in the head is very important, because if the portfolio consists of many coins, you start to follow each of them, it takes a lot of time and the focus is lost.
The first 4-10 years of investing and building an investment portfolio might seem kind of boring because it seems to take a long time to really build up value, so measuring how you are building it up and figuring out your various strategies might contribute towards feelings of impatience and frustration... and like you suggested, if you are investing a few thousand per year because you are still building, it could take you 4-10 years before you start to get to a sizeable amount of somewhere between $20k and $50k.. and where you might start to feel some of the compounding effects.. yet even compounding effects are likely to take even longer than 10 years before you start to feel them in terms of the size of your investment portfolio.
So surely these periods of "down" prices are opportunities to buy - but at the same time, many of us likely realize and appreciate that there are a lot of people who are losing their abilities to feel comfortable investing and/or to feel that they have a sufficient amount of extra cash that they can invest... .so in that regard, sometimes the extra cash is going towards increases in expenses, even the basics food, lodging, energy (utilities/transportation)..
Nonetheless, there are always ways to buckle down and to focus on how to invest, such as investing in bitcoin... or even another matter of various ways to invest in yourself and to attempt to improve your current lot or your future earning potential (if you are young)... so yeah.. strong hands are buying.. but if they might feel that they do not have a lot of cash they also may be figuring out ways to increase the strength of their hands.