Functionality commonness heavily implies copying or standardizing existing capabilities. I think one trap of building platform products is to treat previous functionalities as "this is still very much needed, the same way as it is". Often expectations have changed since something was built. The purpose of the platform capability matters a lot; if you want to create a somewhat different solution, that could reorder priorities.
How does one decide what to say no to for being built in the platform, besides how common is the functionality?
Functionality commonness heavily implies copying or standardizing existing capabilities. I think one trap of building platform products is to treat previous functionalities as "this is still very much needed, the same way as it is". Often expectations have changed since something was built. The purpose of the platform capability matters a lot; if you want to create a somewhat different solution, that could reorder priorities.