Have some doubt on it,
When Bitcoin rises, other coins fall because people are selling their alt coins to go into Bitcoin?
Not entirely true, those who sold their altcoin are only those who wanted to join the bitcoin surge but doesn't have extra fund to do so but those who have money, they never sell their altcoin just for joining BTC trend's sake.
True, there are still investors who stand to this momentum, instead of selling their assets and jumped to bitcoin they choose to stay and keep their coins,
If they have spare money then they'll invest it separately with bitcoin and enjoy keeping their alts and wait for the trend to favor them before selling it
with a much decent profits.