despite the fact that you did not specify any other factors. the person with 1000 wins will definitely win! behind the medal itself with the first place, there is a powerful factor as "the psychology of the winner". What difference does it make to a burned-out person that he loses 1001 times, it doesn't matter for him ?!
This question cannot be answered exactly, you can only describe your opinion. It would be important to know how many "competitions" were held by both opponents. Who knows how many victories a person with a thousand defeats had or how many defeats a person with a thousand victories had? If we assume that each opponent had only 1000 fights (let's say), then I would still bet on who won more. Because for 1000 battles fought to lose 1000 times - you need to be a very unlucky person, and maybe a person who simply does not care about what he does. A person who has won 1000 victories has at least the desire to win them, and this is most often the key factor!