Yes, MongoDB is not necessary for isomorphism. At Hashnode we are using MongoDB and it is working out well for us. So, we decided to use MongoDB in MERN. You can always replace Mongo with another DB like RethinkDB, CouchDB or something else you like. :)

Same as why you need MySQL in the LAMP stack ... you could do the same using PHP and, say, Postgres on Windows using nginx.

What qualifies as a cool stack is the following:

• One tech each for the DB (Mongo / MySQL), web server (Apache / Express), environment (Node / Linux), and the defining framework or language (React / Angular / PHP).
• You should be able to pronounce the acronym, for example, LNMP is no good.
• It's actually something. You can be Mean, light a Lamp or go for a vacation to Mern.

I think MongoDB is adding unncessary complexity to this project (primarily because we have to install MongoDB just to run this). I believe it should be split, e.g. we should be able to specify in the mern-cli that we only want an isomorphic application with Express and leave out the storage layer.

Another reason, this github issue will be repeated many times - https://github.com/Hashnode/mern-starter/issues/18

Front page of the website also states: No configurations and setup. - but this is misleading as it is not that simple.