I have a Samsung Galaxy S7 that I expect to last until the touch screen dies, or I drop it from some incredible height or I begin to think it ugly. I replaced the battery once already. Battery replacement was obviously not intended in the design. But I found patience, and some minor tools were adequate to open the phone up. I did purchase a replacement back in case I broke the original during the process. But replacement battery and plastic back were readily available on the net (approx USD $20-$30.) and as long as they continue to be there should be no problem with maintaining the phone.
I have found that the design is for built in obsolescence based on eventual battery failure. This was confirmed by an app, AccuBattery, which indicates that if the battery is charged only to 80% of capacity then its life span is extended to several multiples of what a battery charged to 100% each time will experience. I can see no reason why a phone cannot be designed/built which takes this into account, only allowing charging to 80% of capacity.