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.
So,holding to me is still the best option for investment in cryptocurrency, especially when the investment is being done during bear market, it will really end up given a very great profit in future, it is best to make short trades when it is the only source of income for one but if it is not, then long term option will be best.