It's not just that, I also believe that people are also just really dumb as I have seen many people try to punch a invuln heavy, over and over and constantly bouncing off and not realizing that it's not working until they die, and even then they don't learn anything.
But in all seriousness maybe give them an Aleph themed glowing effect or an energy bubble surrounding them may help make it more obvious that they are using their Aleph and can't be harmed by melee, but also show newer players that they can still be shot.