Now my question is, is it good for my future that I have sold my altcoins and invested in bitcoins?
Let's say usually, at first, when you're new to this world you buy several altcoins, then you realize many of them are pointless and it's better to focus on BTC, so I would say you made the right choice. The only altcoins I really like are ETH and BNB, those have a great potential and it's worth having some, especially ETH in the short term it may even outperform BTC.
Its true that most altcoins are just a water of time when it comes for using them as a means of investment but I can bodly say this thought doesn't cover for all of them, ethereum like you said is one altcoin that can be reliable when its come for using it as an investment means or any other activities crypto can cover. But in all BTC still superceede them all and thats why many people are realising it and moving their major investment to BTC and this is also done due to the fact the bull season is almost here too.