I believe its harder to be a grandmaster in chess. As much as competitive videogames have developed across the years, it all comes down to the options you (as a player) have from the beginning of the match. Chess involves millions of different posibilities and combinations which branch with every move you make, while esports don't come close to that number. Not bashing on esports, of course, as they usually are more entertaining for most people.
When you consider reflexes and muscle memory, then esports has an edge (as chess doesn't require practice in those areas), but I think that the overall effort you have to invest into becoming the very best is greater in chess.
However, time might change our perspectives. Chess has been around for nearly 1500 years, while esports only started existing about 50 years ago. As they continue to evolve, I wouldn't be surprised if esports achieve the same level of complexity that chess has right now.