Bitcoin and Ethereum are not targets during altcoins season, they mostly move slower and altcoins triggered the massive pumping. Waiting patiently for altcoins season, it a definitely going to appreciate able to see our portfolio pump more harder as never before, this is the time to stack enough prominence altcoins because when the bull comes, we might not have a chance to meetup the high demand of the market. Some traders mostly wait for the bull season, and join the race, making them to be entrapped when altcoins starts dumping.
I think ETH and BTC do not move "slowly", it does move to a point but it doesn't move as little as people think it does. I believe that the best thing to do in this case is to make sure that we end up with a good coin that goes up for sure. BTC and ETH can do that, the altcoins that we buy could be risky and could crash even during bull run if something unexpected happens, or not even go above the previous ATH because of it even if it rises.
However, we at least know that ETH and BTC will do fine, so that type of guarantee beats any kind of pace, sure some alts will go up a lot, and that would be lovely to hold those but that doesn't mean that we will hold them, we could own ones that go down during the same period and lose money too.