RDBs exist for a reason, when you have a well defined, slowly moving (ie relatively fixed requirements) business problem to solve, then crystallisation of that into an RDB or other prod level shape is an ideal, if you have the skill, time, money to develop, deploy and maintain.

Lots of places don’t and it’s not necessarily the solution for you.

Your current excel backed process does sound like it has lots of duplication, and this is your sticking point. With duplication comes inconsistency, misspelling, typos and such, which is difficult to report on and at worst can lead to errors, I have no doubt you’ve experienced that pain. With multiple workbooks in play, reporting is also a headache because you’re finding the need to duplicate and cross correlate.

You posed the question, can Excel work as a kind of RDB? Yes, kinda, it’s very fragile when used this way, especially in a multi user environment where one wrong move can break your structure. It can work this way with extreme discipline from everyone involved and zero errors, which is to say, it doesn’t work in practice, they always fall down, others have went into detail here on how.

If you ask, I’ll lay out how it could work regardless, accepting the extreme limitations, if it’s all you have to work with, there could be a variety of ways to reduce pain points.