MySQL performance over a (local) network much slower than I would expect

It's because if the DB is not on the same server as the frontend you have to do a round trip for each query (potentially more, depending on the size of the answer). It can easily take up to 1 ms to ping another server in the same datacenter. Much less if the two servers are on the same rack, but 1 ms is a good rule of thumb.

That means that for ~300 small queries you should expect ~300ms, pretty close to what you are seeing.

If the two servers are on the same machine, you only have to do some context switches between processes to move the data from the DB process to the frontend. Usually a context switch (with all the typical flushes) take ~40us (very broadly speaking), and you need at least a couple of them (frontend asks for data, DB reads requests and prepares and serves the data, and frontend reads back the data). So I would expect ~80us for each query (let's round it to 0.1ms to make the math easier). You can thus expect ~30ms for 300 small queries, which is also pretty close to what you are seeing.

It's really hard to give you a definite answer. I really don't think the network is the bottleneck, well, unless you have some really heavy traffic on the server.

Do you have the same exact configuration on both your development machine and the production server?

Are you sure that all indexes were created successfully on the production server?

It could the amount of data in your production server. I mean to compare the results between the production and development machines you should have the same number of rows in the tables, is this the case?

Did you use the same installation files to setup MySQL on your development machine and production server? I mean do you have the same version of MySQL on both your development and production machines? Is it for the same OS? Also 32bit or 64bit? Probably a bug in the version of MySQL installed on the server.

The possibilities are endless, without more details it will be really hard to give you an informative answer.