The numbers you present here makes one think things are pretty well balanced against the stealther. If only 5% of the people need the counter skill to handle 50% who have stealth, then it favors non-stealthers. If 50% of population needed the counters to cope with the 50% stealthers, there would be balance.
However, the game does not work this way. There is a near infinite (at least for the sake of argument) number of ways a person can play his character template. There are a variety of tactics for dealing with each of the numerous basic templates. So you can't look at the percentage of some skill and determine whether it is overpowered based on the presence or absence of another skill.
For example; I am a stealther through and through. I get killed the most by a group of 3-4 necro-mages and other forms of mage. The people killing me often have neither detect nor tracking (though I hate it when they are joined by a tracker). Damn tracking is over-powered

.
For the most part, people don't use detect and track because they aren't very effective. It isn't because they aren't needed.
Have you ever run detect and track?
I agree with you that for the most part there are a wide variety of templates and counters to those templates. However, ask a stealther how to counter hide/stealth and they will almost universally respond "Get track and detect."
While that combination may work somewhat against a lone stealther, it is inadequate to deal with groups for reasons already explained.
Again, have you ever run detect and track?
You are getting killed by necro mages? If you choose not to be killed by them you shouldn't be. They have no way to effectively reveal you.
That is the problem with hide/stealth. There is no skill set I have to have against a mage. I can run without resist by using a trapped box. I can counter mana vamp by having mana regen.
There is no certain skill set I have to have against a dexxer. I can counter with a weapon skill, or use a mage weapon, or defend with a pet, etc...
What is the counter for hide/stealth? Detect and track do not work reliably. Conflags have a very limited AOE. Even if you can reveal one, smokebombs are instantaneous.
Look, maybe hide/stealth doesn't need to be nerfed. Maybe it is just fine the way it is. But, if you aren't going to nerf it, then other changes have to be made to balance it.
I'm happy to listen to those. I don't claim to have the ultimate solution. I just know the way it is isn't working.