One other thought: if you pay $80 for $100 worth of stock, 10% decline wipes out $10 of wealth. Your tax savings are someing like 10% *$20 = $2. $2 isn’t insignificant, but you take on a good amount of risk to save it.

This is not correct. A 10% decline wipes out 50% of your ESPP profit, so your tax savings are actually a loss.

In the scenario above (assuming 33% income tax rate vs. 15% cap gains), the breakeven point for flip vs. hold is a share price decline to ~$96.