Not a particularly useful comparison, considering there are relatively few demands placed on Watch storage compared to iPhone. I didn't have storage issues on my 512 MB First Generation Watch. On my 12 GB Series 4 I have 6.9 GB Used, which is almost identical to the 6.7 Used on your Series 5.
Speaking more broadly in terms of human behavior... People have a choices when it comes to living with limited resources. I've lived in fairly large houses as well as modestly-sized apartments. It's relatively easy to keep a large house neat-looking - there is usually empty closet and cabinet space for new purchases, and the impact of a few out-of-place items may seem small amidst those wide-open spaces. Keeping a smaller living space neat requires a more constant level of effort, and some attention paid to whether one has the space for a new acquisition. One is more likely to have to dispose of some old stuff to make room for the new. Even so, eventually even a large home can become cluttered.
Someone who is still using an iPhone 5 may have limited finances, or just have different spending priorities. Whether it's by choice or necessity, a bit of "sweat equity" may be required to live within those smaller quarters. It's not a matter of what someone "should" have, it's a matter of dealing with what they do have. There's no mystery as to how to cope with it.
