Why not both a SD card and 128gb onboard memory? I use a SD card to add additional GBs. I store my music and photos on there. You know some phones don't need a pin to remove a SD card, right? My dad's Revvl requires someone to remove the back cover. It's pretty easy.
Samsung knows it’s target market better than I do. But I think the number of people who actually use more than 128 GB on a smartphone is so small that it doesn’t justify the added cost of an SD card slot. Just have 128 GB and 256 GB models and be done with it.
For the use cases that have been described here so far, it seems to me that there are easy work arounds of either using cloud based storage and/or alternative file transfer methods.