with that logic 51% attacks should not have happened in all these small altcoins that experienced multiple attacks throughout the years! but they did. it doesn't matter if someone holds a lot of the coin or if the price collapses or not, 51% attacks are a plausible one when it comes to small altcoins with little hashrate to secure the network.
in the end it will all come down to cost of such attacks. for example it is extremely high for bitcoin which makes it impossible to pull off but it is super easy in altcoins such as BTG and Verge both of which had 51% attacks recently.