He may have meant that his sins stacked higher than anyone other, not that he currently sinned more than any other. Personally, this is what I think he meant.1 Timothy 1:15
This is a faithful saying and worthy of all acceptance, that Christ Jesus came into the world to save sinners, of whom I am chief.
and if you have any question. In the greek am chief is present, active indicative first person singular.
so did Paul contradict himself?
Much love!