Every investment comes with risk and the same applies for bitcoin too and you can never say I am 100% sure that bitcoin will be higher in the next 5 years from the current price and it will likely to be but my point is there's always risk factor in it which creates pressure for retail investors.
To minimize this risk they also should follow diversification, if they can invest $250 a month and no more than that then I recommend that $100 for bitcoin and the remaining for other things they consider potential too grow which reduces the risk and able to have a peace of mind even when the price of bitcoin is crashing because I can't imagine all my savings is in bitcoin and it is crashing 30% in a day will surely creates a panic situation that might force some of them to sell that will result in a capital loss and wasting few years of investing.
Diversification is also good and am not against it. One is free to do other investments outside Bitcoin which your you have sound knowledge about and which also predicts future gains as you studied it too.
Diversification to shitcoins is never good no matter how much study you put into it, it will amount to building your mansion on quick sand. Why would you even contemplate diversification when Bitcoin is all you need to be ok? The money you want to throw away can get you a good portion of Bitcoin and improve your portfolio instead of giving it away to shitcoins that is usually overhyped. As a new investor, never have any interest in shitcoins so you don't make the mistakes that some of us made that made us waste money we would have invested in Bitcoin and be happy by now that Bitcoin have gone above $100k.
Let me be honest with you, if you focus on buying Bitcoin aggressively for 15 years from now, you will be one of the happiest person on earth and you will be proud of that action.