I humbly disagree. If people want to hoard, they can simply use other liquid assets for this purpose. These assets do not need to be usable as a payment method. Why should a decrease of price level turn people into misers?

What causes disturbances are unpredictable changes, e.g. changes in the changes of the price level (i.e. second level derivative of price). That might, for example, shift the attention of hoarders between money and other liquid assets and disturb some businesses. But eventually, people's expectation of price level changes and the current price of money will equilibrate. Bitcoin is highly resistant to supply side shocks, so mostly only demand side changes affect the price.

I humbly disagree as well. A disruption might cause this when the prices take a while to adapt, and a shortage of money appears. But unless the prices are regulated, this wouldn't take long. After the equilibration, the mismatch between demand and supply decrease, and there will be again less reason for competing currencies.

Here however I can agree. An alternative currency can smoothe the equilibration of the prices, or speed it up. But it's not inevitable. Derivative markets (short selling, margin trading) can have the same effect.