I converted all all my altcoins to btc and eth and solona and stop listen to youtubers.
The youtubers can ruin your life. make your own decision and you will be fine.
This is relevant for me.
ETH and Solana are also altcoins. You are lucky that you made a good decision at the last moment of bullrun which many could not. But I think it would be better if you could convert your assets to USDT. Because btc, eth and solona are also bleeding.
Maybe what he mean is alts that aren't good as the three. He have done a good job there, now that there is still a bull because if not and the bear takes place, those other alts he have won't have a chance to recover anymore but yes many won't do it because for them profit is important first before any other things so what they do is they sell their coins for fiat during the bull run and they will only re invest again once the bear takes place.
Your idea of converting volatile cryptos is fine but I would choose a better stable coins not usdt because many says that it is risky. I would got for busd, usdc and dai, as I never heard any negative feedback from them.