Bitcoin dominance will not let the altcoin season to start and make the altcoin lovers rich. It will take time at least for 2 years to see stable growth. The stability is still the biggest problem but volatility also help Bitcoin to gain more attraction.
in my opinion if selling all Altcoin for Bitcoin is not the right thing, that means you will lose all Altcoin by getting Bitcoin, and the price of Altcoin is very low compared to Bitcoin.
it's better to wait you can get a big advantage from Altcoin, and after that you can buy Bitcoin with the results of profits from Altcoin, maybe it will be better, Altcoin can also be profitable depending on the growth of Altcoin you have.