It doesn’t seem like you’ve considered that people do a better job discerning sarcasm in person than via the written word. In person, you can judge tone of voice and facial expressions. I once heaped praise on someone by email, and they became really upset, because they thought the email was dripping with sarcasm.

Including the “/s” helps to ensure that one is understood. To me, that seems more important than whatever it is you think has been lost.