altcoins are centralized assets, while bitcoin is a decentralized asset,
Not all altcoins are centralized. Some altcoins are decentralized like Ethereum. The difference is you can't point out the actual person, people, or company that created Bitcoin but you can point out the people or company that own every other altcoin.
If you ask me I will say only buy Bitcoin but I see why latecomers are attracted elsewhere, there are other cryptocurrencies with unique features & potential for large growth.
I feel when it comes to long-term investment, Bitcoin is the ultimate. There are no single altcoins I'll comfortably hold for a very long time, but for a short-term investment, nothing wrong in banking on a few very well-researched altcoins.