its simple, sell your ethereum now because you already got a good profit and buy bitcoin, if you only believe in bitcoin for long term investments buddy
Actually even though it is not sold right now it will not be a problem for him and he can also sell other Altcoins to buy Bitcoin which has twice reached its ATH this year, so in general both of them are very good to hold in the long term, both Ethereum and Bitcoin.
Most of the people who are not used to trading bitcoin will panic when they see a correction. that's the reason many prefer lower-value altcoins.
bigger profits might be obtained in bitcoin but when a correction occurs the big losses are there too.
to be honest I prefer to store ETH than BTC. it's not because of its value. but my ability to analyze the ETH market is better than BTC.