The best way to explain this might be to relate my site to a comparison shopping site, as I have around seven tables with 500k+ records each. The content on my site is a comparison of items, and involves variable MySQL queries to create the "content". I imagine there is a way to build database intensive websites on WP, but I have not been able to find the answer thus far.
It's not complicated to connect to custom tables in WP context and query them, using native
However "not complicated" is about all there it. WP API functions are primarily aimed at querying its own data structures. While
wpdb does have some helpers, they are simplistic and not meant for more elaborate custom queries.
Another issue is that by implementation
wpdb drags all of query results into memory immediately. This is Bad Idea for any queries that return large amounts of data. WordPress backup plugins (which are query-intensive by definition) typically have to implement their querying from scratch, otherwise they just crash on large sites.
In a nutshell WP won't help you much with this kind of site. If you have other functionality in site that WP is actually good at, then it might be a possibility (since you will be implementing much of it yourself in any case).
If this is your site's main/only function you are likely better off considering alternatives first.
Some time ago i would think that this is a valid thing you can ask from wp.
But now i think it is not.
I would choose Laravel for example over wp for what you seek. WP is NOT a full framework for line of bussiness apps.
Off course you can do what you need with WP but in the end you would wish you used something like laravel....
If i was to give an answer i would say that you have either to use core WP with custom post types and taxonomies to build your app or you could use your own custom tables.
Also a third option could be to utilize both and mix custom post types with custom tables....
Have in mind that you dont have an ORM at your disposal with wp...