"Relational" databases are much cheaper comparing to MongoDB atlas.I mean $50k per month cheaper. Also AWS documentdb doesnt natively support 128 bit decimal ...

The performance boost was at least 10x and even more with complex LINQ queries all thanks to entity framework. At that job, we did a lot of risk analysis, bucketing bonds and creating a composites. Entity framework core and it's LINQ to SQL was a key in performance boost. Not to mention entity framework provides multiple layers cache which we used as our risk analysis algorithms were basically custom version of bin-packing ...