I agree that "hedging with Bitcoin" can be a tricky business....
And when BTC risen from 800 USD to 20000 USD, in 2017. With that type of gains, most people are chasing 10x....20x....or even higher gains! Which can be a trap, as you said altcoins are very heavily correlated to Bitcoin. When BTC is on decline, most often altcoins following with the price too.
Then people panic, and sell their alctoins, for cheaper BTC, or even worse, they are holding those alctoins, and just watching the price declining.... their portfolio shrinking.
Worth to mention: most of altcoins had their all time highs in December'17, and lost lots of their price value since.... some of them might even never recover.
This is the reason, why knowledge and market research comes into very useful play. Whether you are a trader, or investor for a longer run: knowledge, and investing in really good projects, with great team, MVP, profit generating systems behind - are the best option when investing / trading (this reducing risks massively).

On the other hand: if you know how to hedge altcoins vs Bitcoin - this can be extremely profitable.