I do not think any blockchain could replace ethereum so soon. No one knows what will happen in long term but I am more bullish in eth than avax. There are other blockchains Solana, Cardano, Polygon, Decentraland, and Helium which have been done better than avax in 2021. Do not look at the price because it doesn't reflect the project's future potential.
Yes, that may be, but it is well known that Ethereum has a major problem: The fees. On Uniswap, a simple swap on the Eth blockchain currently costs between $100-$150 in fees. This is insane, unsustainable, and opens up opportunities for competitors. One of the ones I see for this is Avalanche. I think it depends on Ethereum 2.0 whether Ethereum can maintain its position or will be overtaken by others.