Table separation leads to record fragmentation and big IO cost on record fetching. Your ideal academic world will be crashed under production reality. "Millions of records". Bwa-ha-ha.
If your DBMS is so poorly written that record fragmentation is an issue then you need to change the DBMS. Since most (>99%) of the database design and implementation work that I have been involved since the mid-80's was business related and for a variety of different industries, I didn't find table separation to be a problem. The appropriate designs led to faster applications.
I have also worked for companies that didn't use relational database theory for their products and they had far more issues. In a couple, I was able to hive off the database designs from the main systems and got the applications to actually work and work properly.
