I find that many people have a habit of holding ETH, BTC, altcoin for a long time and always hoping that it will rise again. If you are a trader, you will lose money for that. Set small target and sell them when you see profits. I only need 3-5% profit when trading.
If you see the market going down, stop loss before it's too late. You may lose 5-10% of the capital but when the market goes down you can buy more btc, eth when you hold btc, eth, altcoin.
Sell all ETH, BTC into Stable Coin when the market goes down
I don't think it has any problem, if we hold ETH and bitcoin for a long time, these are basic coins of crypto and if we want to big profit from them, then we must need to hold them for a time.
As you said sell the ETH and bitcoin when market down, i also disagree with you, when market down then we sell them, we are doing double mistake. When market down just hold them, with a passage of time, definitely ETH and bitcoin give us triple or more than it profit. Now you could see the bitcoin price has started to go up.