Assuming that one had a significant amount of cash or cash equivalents to pay the taxes, have enough to do so over then next "n" years worth of conversions, and if they are using the cash bucket strategy, do not dip into that bucket to pay the taxes. Those are a fair amount of if's to consider beyond a simple statement of "better" IMO.
Not everyone is in that camp. I am not. I have read on this site that others are similarly situated. Most of our retirement savings are in IRAs or 401K's. Personally, I am currently trying to maximize my IRA withdrawals to minimize eventual RMDs. These RMDs will push me into the next tax bracket. The more I can get out now while keeping in my current tax bracket, the lower those taxes will be. Possibly keeping me free from increased Medicare premiums (IRRMA).
I hope this makes sense to you.