I cannot counter all what you have listed,it is based on what you believe, nice one tho, but let me say something. Diversification is not always a necessity, their are people who wants nothing to do with Altcoins, like they do not give a fuck if the price of this Altcoins skyrocket so they have nothing to diversify, they believe solely in Bitcoin. We consider the implementation of diversifying our investment when we dealing mostly with lots of Altcoins, since there is high risk of losing funds. It Is considered wise for every investors to hold good portion of Bitcoin before thinking about diversification, we diversify our Altcoins investment not on Bitcoin.
You are totally correct and this kind of mistake makes most investors to later regret their actions of solely believe in Altcoins even knowing the high risk of losing more funds even though it also increase in price at times but solely relying on Altcoins is not an option but for me I rather invest in Bitcoin than Altcoins because it's a waste of time and energy although Bitcoin also fluctuates at times but can't be compare to Altcoins and it's more reliable. Although the choices is really based on individuals but no matter any one chooses, let them be aware about the risks involved.