While there shouldn’t be any major performance difference between these two endpoints, I should note that the Participants Report endpoint falls under our Heavy rate limit category, so you will be slightly more limited in the number of requests you can send to that endpoint per second (vs. the past meetings endpoint, which falls under our medium category).
But in terms of the actual performance of each endpoint, these should be comparable.
The other biggest difference besides the response body, is the reports endpoint you have to call with an Admin level OAuth app, but the meetings participant endpoint you can call with either an Admin or User level OAuth app.