The only altcoin that do not have the chances of loosing value are mostly some of the top altcoins we already have in the market. Anything more than those, get to be under probability while investing, that doesn't keep the investor at peace because he never knows if the altcoin could worth more while holding or reduce to a point where even recovering back the invested amount is impossible. Bitcoin offers this comfort, no matter the price reduction, there will definitely be a good bull run and profits is made.
Profits do not only depend on the kind of strategy used, DCA or not as long we buy and hold Bitcoin, we must make profits by the end.
You already said that BTC can experience a price reduction, so therefore don't say that alts doesn't have the chance of losing their value. Even though they are only alts, they are still part of a crypto market and we know that this market is so volatile. So even if we picked up the top coins, there will still be a little stress that we can feel.
It's normal though and there are still practices to reduce or even prevent them from occurring. So as long as we gained an experience, things are going to be easy eventually.
Bull run is for all and not just for Bitcoin, this is why it's also not wrong to invest on other coins or make a diversification, only if we want to pump our profit potential.