To be honest I thought I needed e-sim on my watch but in the end it isn't a necessity for me
Everyone is different but considering 99% of the time we have our phones with us I don't think it's the end of the world. Nice to have, yes, a must? No... Not yet I don't think.
You're obviously not a runner. I run some quite long distances and I love the piece of mind that I get from knowing that I can call for help if I have a fall or some other type of accident. It's the main reason why I use an Apple Watch instead of the Garmin Forerunners that are more commonly used by runners.
I'm not sure why Samsung watch users need it though. I do several marathon events every year and have never seen any runners wearing a Samsung watch.
As a mountain biker who doesn't like the idea of crashing and demolishing a $2k iPhone, the eSIM for my watch was an absolute game changer.
I also used it while paddleboarding yesterday, so there's that too.