a) Just heard today: JOINs are bad for performance b) How many columns can (an Excel) table have: no need for JOINs

Wow, I'm sorry you have to work with such coworkers. For reference, joins are just an expensive use case. DBs do them about 10x faster that you can do them by hand. But if you need a join, you probably should either a) do it periodically and cache the result (making your data inconsistent) or b) just do it in a DB. Confusing caching the result with doing the join efficiently is an amazing misunderstanding of basic Computer Science.

vlookups are bad for performance. recursive vlookups even more so.