Is Ethereum and other altcoins taking over and replacing Bitcoin?
What do you mean to “replace” it? What is Bitcoin to be “replaced”? That it'll stop being the #1 on market cap or that people will stop using it? Because I highly doubt for both. Bitcoin was the first one, it was the one that started this technology.
I'll quote you a nice part of the nullius'
Social Phenomenon:
People who disagree with each other about everything else, can agree about Bitcoin. That is what gives Bitcoin its value: Everybody wants Bitcoin, no matter what their opinions about anything else!
Besides the above, there are others
more practical reasons why Bitcoin will always be the default one. It is the most decentralized one, with no premined coins (such as with Ethereum) and with a dedicated developing team.
And as said by others, you shouldn't be comparing Ethereum with Bitcoin since they're solving different problems. It's like believing that oranges will replace apples, because oranges taste better to you.