What is strenght for you?
Don't get me wrong: both interpretations are true. That's what muddles it.
It is true that a fighter can have greater physical strength or brute force, and thus be stronger, yet be incapable of beating someone more skilful, who would then be the stronger fighter. See, muddled.
In this context, "strongest" clearly means "who would win in a fight", not "who would lift more or win at arm wrestling". Which is why Zoro has to
defeat Mihawk in a duel to gain the title, not surpass him neither in a skill showoff nor in an arm wrestle.
It is also true that both physical strength and skill can only carry one up to a certain point, which is why characters like Shanks and Mihawk for sure have a lot of both, but likely more skill, unlike Kaido, who focused more on his natural overwhelming strength (yet still had proper techniques and even improved his CoO to proper FS).
On that note, Mihawk is known to equally use a blade of strength and a blade of gentleness, making him very balanced in that regard.