MongoDB is definitely ready and capable of handling your traffic. There are best practices to follow, however, as is the case with any deployment. I would concur with mattbillenstein that HN definitely skews anti-mongo.

There are many, many companies using MongoDB very successfully. I have found that "issues" being reported with MongoDB are based on old versions and information, or an improperly configured and tuned environment. I recently wrote a blog post covering some topics around this. I'd encourage you to read it: https://www.kenwalger.com/blog/nosql/mongodb/mongodb-perform...

I think you'll find that MongoDB will meet, and exceed, your expectations for performance.