So, let's look at the counterarguments again:

- you can't just buy 15% of the hash rate
- miners wouldn't just shut down and make an even higher loss, because the bought costly hardware they now don't use.
- even in an event of 50% hash rate loss, that just means 20 min for a confirmation and 4 weeks for an adjustment and than it is back to normal

The only argument you bring in here is some kind of network effect, but you just can't predict, how other actors would react.