FLEXIcontent is a generic component for content management which sits on top of joomla, this is a bonus of not canceling joomla and ...
Joomla itself is partly normalized but you are using it.
About, the way the data are entered in the forms, it does not mean, that they are entered the same way in the database. And we cannot easily change database, a lot of code updating will be required , plus compatibility and upgrade / downgrade issues etc ...
Anyway the redundancy in FLEXIcontent db is rather small, THERE ARE TABLES FOR RELATIONS and is not worth tampering with to make the source code more complex !!!
Now about performance this is a big topic too, the database size or queries might not be the only problem, e.g. joomla plugin system will call all "listeners" registered to an event even if you want to call specific plugins only (the FLEXIcontent choosing of content plugins to call for a FLEXIcontent field, unfortunately
calls all content plugins loaded up to the pointing of calling, so it calls more content plugins that those you choose).
For FLEXIcontent fields (aka plugins) the new FC versions bypass joomla plugin system to call plugin functions directly, the gains of this is small, since inside the plugin function of FLEXIcontent field (plugins), we have a check that returns immediately,
but for content plugins this is not the case, since they are made to execute always on a particular event, and if we can bypass joomla calling of content plugins, to call specific, plugins the performance gain in category view will be big.
I have done this 95%, but i need to finish and include it next version.
About being more flexible/convenient i don't know since FLEXIcontent has
-- smart heritage of parameters e.g. for item:
a. Global params
b. Category params (new !!!)
b. Type Params
c. Item Params
-- Easy to track templating in items / category manager tabs (and will add more too)
-- Massive copy for category parameters
-- (will have) Massive copy of items parameters
The above are very useful when managing a big site.
Anyway if i had or make an installation of 100,000 items i could profile it and find bottlenecks to optimize (i mean more towards code and queries and less towards the database schema) anyway as you say there are other components that maybe more suitable if you have this site.
Best Regards