I feel like you guys aren't disagreeing with each other?
Optimal strategy for most people would be owning a diversified portfolio, regularly buying with available funds (holding back only enough cash to act as an emergency fund), and slowly de-escalating risk as you approach retirement by adding fixed income to decrease volatility.
Having cash on hand to buy dips almost, by definition, means you haven't been following the above strategy. You've either sold assets to hold the cash out of market or have been avoiding investing all available funds to have a slush fund ready to deploy - both of these are forms of timing the market.
Time in the market beats timing the market.
Now, there are for sure points of debate in how to go about the above strategy. What does a "diversified portfolio" look like? What does de-escalating risk look like? What percentage of equities should one hold on retirement?
Some people for sure make money by actively trading, but most don't. Even people that index invest tend to worse than the indices they are tracking. Human psychology is our own worst enemy.