For example, someone told me it's nonsense to hold btc and ltc, because ltc follows btc pumps/dips and I should only hold 1 of them.
Should I consider adding a privacy coin?
Or even more "platform" coins like eth?
This is bullshit, pretty much every coin follows btc. Except if some coin is pumped or has some major update. You can make sure of this by going on coinmarketcap and see what happens now, when btc is dropping.
Well this can be true about a couple of years ago. But time has changed buddy. Not every coin now follow the pattern of bitcoin. Heck, in December alone, all coins are enjoying their best year so far. So that's mindset no longer applies to the current state of the market today.
My only comment on his portfolio though is put more money on bitcoin. You mentioned privacy coins, Did investing on Monero cross your mind? Another good coins for me to put some investment on it. And yes, ETH is one coin that I would love to invest as well. Just saying.