Is it correct to store customer data in Bitrix CRM?

Question

CRM

There are 12 databases of source systems with customer transactions (there is no single ID), there are marketing attributes (UTM tags, communications with customers) that are now stored in Bitrix CRM. You need to connect all this in order to see the client's history, frequency of purchases, channels, etc. We argue with the developer (I am the PM) how it should look:
Developer: all data must be taken from the databases and stored and cleaned in the Bitrix database, it's easier that way.
I:All data must be consolidated and cleaned in a separate database, where customers can be matched and assigned a single ID. CRM must transfer marketing attributes to this database and then pull transactions by client ID. And it is also desirable to put an ETL system in front of the database, which will correctly clean and reduce data. Storing all data in the Bitrix database is unsafe, non-scalable, loads CRM and is dependent on software.
Who is right?

Answer 1

... Some kind of nonsense, or maybe I didn’t understand ... Well, for example, we have Bitrix24 only as a lead management tool, the lead ended (with a deal or a refusal) - everything goes to 1C, and 1C is on a separate server far away ...