I have being giving this question a thought for days now, if other altcoins can be a threat to bitcoin especially ethereum
ethereum has not had its own independent community. just look at how much ethereum mirrored bitcoin 2021-2024

this was because bitcoin is the main coin and due to arbitrage opportunity of [USD:BTC][BTC:ETH][ETH:USD]..repeat
it allowed people to use ethereum just as a circuit/circular path back to bitcoin
meaning most of ethereums price action was due to bitcoins actions, ethereum doesnt really have its own economics to have its own major events to be different to bitcoin
you can see from 2021-2025 on the BTC:ETH chart that ethereum pegged its best rate at 1btc:12eth in 2022..

but then has been slipping and losing its quality of pairing and now sits at 1btc:40eth
so ethereum is slipping away and becoming less important
in short ethereum doesnt have:
its own community to give it its own speculative market
a strong peg-pair to bitcoin.
a worthy minting cost.. it went to PoS which meant underlying value support dropped by 95% so now has alot of room to fall.
any reason but bitcoin to explain why ethereum remains at a bubble high.
bitcoins underlying mining cost is strong giving it a strong value support so not far for bitcoin to really fall but alot of potential to rise