I believe you are approaching this inyan from the wrong perspective.
It is only because they were disciples of Rabbi Akiva who promulgated that concept of "ve'ahavta le're'acha ka'mocha zeh klal gadol baTotah" , that they were punished for this.
They were gedolei oilam! The world was plunged into darkness when they were gone. We are obviously referring to tzadikim of the highest caliber and hkb"h is midakdek k'chut hasaaruh by men of such caliber. So we can assume that the lacking of respect was so minimal that they themselves were unaware of it.
Sadly, as gedolei oilam, and transmitters of Torah to the next generation, hkb"h did not allow them to be the conduits for hamshochas hamisorah to their talmidim.
Instead of asking how harsh the punishment seems, a person should become aware of how devastating belittling another Yid is perceived by the Ribbonei shel oilem.
I once heard from Rabbi Gershon Weiss shlit"a that he grew up with many friends who eventually turned out to be roshei yeshivos and poskim. When he sees his friends of 50 years, does he approach them with trepidation and exclaim "how are you harav hagaon hagadol"? No! He says how've you been Naftali?! But when he thought about it, he asked himself is that the proper respect to accord a gadol baTorah? But we've been friends for 50 years and grew up and learned together in yeshiva!
This explains Rabbi Weiss, is what happened with the talmidei R' Akiva. They all learnt by Rabbi Akiva together and were great friends. But as the grew in their learning and avoda and eventually became gedolei oilam, their yachas to each other needed to change as well. We are now talking to gedolei oilam not only your childhood friend, and that requires a different kind of respect.
Hope this helps put it into perspective.