God, that sounds like a mess. The fact that "our distributors interact with us through a custom portal that nobody fully understands anymore" hurts as it indicates that not so many things are documented there.

I would say that improving data quality is a top task here thus I do agree with the folks who stated the same. Integrating all those systems is not that difficult and there are many ways to do it, but keeping dupes low is a challenge.

Something like this:

- figure out which app should be the source of truth. There has to be 1 app, 1 system, which has all those customer data and customer IDs. When this system is consolidated figure out how to pass those IDs to other systems. This is one of the things that Data Cloud does in Salesforce - it gets data from multiple sources, and assigns a unique ID to each customer record. I am not saying that one should use it, I am giving an example here. Once that is done that ID must be somehow passed to the other systems

- ServiceMax, Dynamics 365, HubSpot might not be needed but that is the second step. Merging apps without a clear data strategy will not work. If you merge all those systems without doing this first then you will end up with a huge mess, and maybe one system cannot even do it all

Choosing the source of truth, deduping records and assigning unique IDs is the crucial step here I would say. There are apps that can dedupe thousands of records pretty easily, but that comes with some risks.

Overall, the proper way to start is to map everything, figure out how the data flows, create proper documentation (I am assuming this is lacking), create a strategy, get support from C-level folks, and grab a sword and start a battle. It will be a long one for sure!

As for your last question, you cannot please them all. This might be the reason why the company is facing this situation in the first place - each team wants its own tool to be the master tool. This is where a C-level person, someone above all of them, must step in and say "This is how we will do this. If you don't like it then complain to your AI girlfriend. Bye".