Hello, and welcome to the party!
There's a lot to unpack there, but I'll try to help a little. These are the questions I spotted.
- Are data warehouses older technology?
At this point in time, yeah, the concept is more than 30 years old. However, that doesn't mean you can't use a data warehouse to solve certain kinds of problems. In fact, it means that the data warehouse solves certain kinds of problems, directly around data reporting & analysis, extremely well. It's possible that a warehouse is needed in your case, but let's talk about that a little more farther down.
2. Is ETL, specifically SSIS, only used with data warehouses?
Nope. I'm not an ETL expert, but I've worked with SSIS and other processes over the years in support of those who are. No, ETL is about data movement. Yes, that might be data into a data warehouse, but the key is data movement. I've also seen SSIS & ETL processes used for moving data out of warehouses and into OLTP systems and data marts. It's just about the movement, not the source or the destination.
3. Is SSIS difficult to learn?
Again, not an SSIS expert. However, the basics, yeah, they're pretty easy to pick up. Then it gets hard. At least in my opinion. Others may disagree.
4. Can a data warehouse help with disparate data issues?
And here things get interesting. So, spreadsheets are good for consuming data, data analysis, stuff like that. The problem comes when spreadsheets are used for data generation. They're just not great. If we're looking at a situation where people are literally inputting information, names you use as an example, into a spreadsheet, it can be very problematic. A better interface for data entry can be built. It can use lookups against existing data to ensure that the names being input are names that are in the system, or, conversely, that the name isn't in the system and needs to be added. This part of your question is a HUGE topic and could involve a lot of discussion.
Personally, I'd say, no, a data warehouse is probably not the right solution here (although, I'm more than willing to listen to why I'm wrong on this one). It seems more like you need a front-end database with well designed input screens to ensure that you have referential integrity on your data.
I hope some of this helps. Welcome again to SSC.