maybe this coin will be at a stable value in the future, but not for new ATH, so to start investing here of course you need to prepare other coins too, so that we can maximize every existing investment, so that the conversion loss can be exchanged at another coin that moves.
But if you choose one coin, this will have an impact, if there is no increase at all, isn't the investment made solely to make a profit, therefore another coin is needed to cover any decrease that occurs on a particular coin
Plus, SOL already faced trouble and feedback about how it gets frozen when there is a big deal going on in it. All of that 65k TPS turned out ot be a wrong thing and it doesn't reach those levels at all, not even quarter of it. This is why a lot of people left SOL and found other stuff, like Avax which can sustain bigger transaction amounts.
Basically, I do not know if SOL would ever be the type of coin you would pick for just one investment, if you have a vast portfolio then having SOL in it doesn't really bother me, that would make sense actually, but if you are going to invest into just one thing, then having that thing to be a big risk, criticized thing would be bad idea.