Most crypto's can only be bought with Bitcoin, so when Bitcoin increases value in dollars then this applies to most altcoins as well.
The way I see it, if you put your money in the right altcoins, you profit double because you gain $ when btc goes up but you also gain value when your altcoin goes up. Ofcourse, if you pick losing altcoins then Bitcoin may go up but your altcoin may go down. So it's a bigger gamble but also bigger gains to be had.

I see Bitcoin going over $4000 for sure at some point, so you may end up doubling your money. But you have to ask yourself if it's not possible to get much more than double your money by investing in altcoins.

My suggestions is to go 50/50 whenever in doubt.. Just keep part of your crypto in Bitcoin and the other in altcoins. Then whenever you spot a superb oppurtunity to buy something cheaply, or a new altcoin, you will have funds ready to buy at the most opportune times. This way you get the best of both worlds, spread the risk around