MongoDB as a company is growing 20% y/y and 2B in revenue.

So very far from being a legacy product.

I still use it for new projects because (a) Atlas is genuinely a solid offering with a great price point for startups and (b) schema-less datastores have become more of a necessity as our control of data has decreased e.g. SaaS companies dictate their schema and we need to accomodate.