It also depends on the person. There are some folks who can't take a hint, there are those who can read between the lines and appreciate the sensitivity, and there are others who simply won't listen to what you are saying unless you bring data. I'm a fan of starting with what ifs and how abouts, and failing that, moving to a more direct approach. The latter is no fun, and usually ends with someone getting hurt, but with *exceptional* techies who know they aren't always right there can be little to no collateral damage.
With some people who do feel they know better than anyone else it can be easier to appeal to that
narcissism expertise. Give them the floor to speak, listen, and then chime in with the how abouts and what ifs. Build that ethos, pathos, logos squishy stuff before you go and poke at their vulnerable spots.
If it can wait, be gentle and coach as needed. If there is imminent danger, then be direct.
It just depends.