Given that SAP modules are architected and managed by SAP itself.
However, small changes are possible at the customer's end.
How can an ABAPer on the client's side take the role of an architect at SAP that designs SAP modules? So what does an architect at the client's side have left to do?
Given that SAP modules are architected and managed by SAP itself.
This is only partially true. The large system design is done by SAP. However many organizations have custom implementations of some sort.
There are often required changes, whether small or large, that fit business applications into SAP. Or custom requirements for the business applications which are caused by SAP.
In an ideal world, you could easily just fit your applications that the business is developing (whether SAP transactions or a system feeding SAP). That process takes a fair bit of architecting.
However, small changes are possible at the customer's end.
You are (likely) kidding yourself if every customer implementation is identical. Unless someone is starting a business from nothing, where they can design their business around SAP's system.
Someone needs to make sure that the SAP design is correct. Understanding how pieces fit together.
How can an ABAPer on the client's side take the role of an architect at SAP that designs SAP modules? So what does an architect at the client's side have left to do?
So, the key piece is understanding how everything fits together. An ABAPer might understand this - but might have a very limited scope of experience. A good architect will have enough experience to see how pieces fit together, so when decisions are required, they can properly evaluate and identify the right decisions - and make them.
It is likely that an ABAPer on the client will not have this experience/broad system understanding. If they do, then that's great, but likely they will not.
An architect should be doing design types of work - not implementation work. An ABAPer is responsible more for implementation.
In my experience, there is a lot of flexibility at the clients end. The software needs to be used in different new ways for new business cases. Someone has to design these usages. That's what an architect at the client's end is for. Is that answering your question?
