MongoDB 4.4 seems to be a lot slower in data load and queries

There is also bunch of other interesting data - MongoDB 4.2 seems to have quite a regression going from single node to Replicaset while 4.0 does not.

Very interesting article.

Interesting

4.4 is still a release candidate not a production release.

Yep it is. The article mentions that. Note though there is quite a regression between MongoDB 4.0 and MongoDB 4.2 too.