Except that is not how things work. The coastline of the Eastern US is determined by sea level. A rising sea will make the barrier islands retreat inland. How much retreat? a 26 inch rise could mean thousands of square miles of the USA that will disappear. Multiply that by every coast on the globe...You said "if all three are the same, then climate isn't changing"? If all three are NOT the same climate must be changing. Small changes in global climate can have small changes in sea level and we already experience coastal flooding in many cases. Any rise in sea level will compound an already dangerous situation.
Here's the latest research on sea level rise ... Climate-change–driven accelerated sea-level rise detected in the altimeter era ... this study gives the upper bound of mean sea level rise at 26 inches between now and year 2100 ... any claim of sea level rise more than this is NOT based of data, and should be considered pure fantasy ... come this January, at either full or new Moon, head over to the coast with a 26 inch stick ... at high tide, put one end of this stick on the sand where the highest wave reaches and the other end straight up ... now level across and see where this highest wave and the highest tide will reach 100 years from now ... right, nowhere close to the existing sand berm ... do you honestly think your great-great-grandchildren will care ... or do you think they'll be more worried about these 80-year-old dumps they live in? ...
Bonus question: Why January? ...