I think they should...I mean when it has come to my iPad and my iPhone, my iPad MAY have around 20 GB on it, while my iPhone is usually 6-8 GB under my capacity (128 GB model). I fill up the capacity of my iPhone because I am way more mobile with it, using it for pictures and videos (from traveling to concerts to events/functions). I would rather have more capacity instead of having to worry about uploading to cloud services so much for my iPhone.
If Apple makes 128gb, 256gb, and 512gb, I would be more than content with those iPhone 8 models. An iPad is different than an iPhone because iPads are built towards heavy-duty productivity in an iOS sense.