Many regret that they invested in Altcoins and not in Bitcoin when it was $ 3,800 a month ago. Such people are not enough. And this is just one example of thousands. It makes sense to invest in Bitcoin because it will only become more expensive in the future.
Bitcoin as well as few altcoins, both are profitable, that is what I think and I have seen. Bitcoin's movement is just noticeable because it is usually a big movement. For altcoins, it just follows Bitcoins movement and the profit earning is slow if compared to BTC.
Personally, I enjoy earnings both from BTC and selected few alts. And would continue to invest in 2019 as well.
BTC is under tremendous pressure with the drastic downfall from ATH and all negative news but I think people will continue to invest, trade, use and help it grow eventually.