That is definitely true, it's not good enough to secure yourself against a persistent attacker but I do think it's a good captcha:

It's a topical captcha that the target audience of the site will recognize and most likely enjoy.

It's significantly different from any other captcha so that automated untargeted bots will not be able to beat it

It has a high enough entropy that untargeted bots that repeatedly attempt to guess the answer will fail

People without a chess background most likely have to think about the answer in a way that makes buying human workers a less attractive option (maybe)