There is no doubt in the long term for Bitcoin. We've seen it already. Those who have planned a long term hold a decade ago, they're already in massive profits.
Even when I started back in 2015 bitcoin was hovering around 600-700$/BTC and now it is 112k USD which is a huge jump. So in one decade it has increased so much, we can only assume what is going to happen in the next decade.
Altcoins have followed suit only. None of them are leading the market. If you are entering into altcoins, enter at your own risk, bitcoin is no doubt safest in the long term whatever price you buy at, but I cannot say the same for altcoins.
Short term gains is a different topic of discussion and altcoins might do well in that, but that is risky and I dont recommend it to anybody.