As someone who plays Nader quite extensively and uses martyrdom with some success let me chime in (obiously I will say it’s fine).
Martyrdom doesn’t need a cooldown Nader already has limited access to it. To be specific the only time it is avaible, is in the short span between getting incapicated and getting gibbed/respawned (she can’t just jump into a spawn and press a button to kill everybody you have to kill her first).
Furthermore B.Montiel brings up instadom (love the term btw.). That right there shows that martyrdom isn’t just a skill-less instadeath button, that takes away your hard earned victory. See Martyrdom is all about situational awareness.
A Nader that always instadoms is a bad Nader.
Sure in some situations you have to instadom or the chance that you catch a knife gibb or the enemy gets away is to high.
In other situations instadom means pointlessly throwing away any chance of a revive, the chance to kill someone with martyrdom a second later or if FF is on they might even TK (I’m a fan of FF-on).
Naders have to judge their surrounding even when they are dead. Every other merc can breath easy for a few seconds when they die (except maybe Phoenix). The moment a Nader dies she has to decide instadom or not if not she has to rotate her view into the best position and stay alert judging the distance between herself and aproaching enemies hoping that noone gibbs her.
One thing that makes this bit harder then you might think. Is the fact that you are working with a black and white view. Making it harder to judge if that is a friendly Aura coming in for the revive or a enemy trying to defib finish you. Thats how you end up with situations of Naders blowing themself up (and the Medic in FF-on) when they get revived (personaly I say sorry when that happens).
Martyrdom is all about judging the situation right. Nader has to do it to use martyrdom effectively and the enemy has to judge the situation right aswell to avoid getting killed by Martyrdom (obviously a good Nader tries to play in a fashion that the enemy missjudges more often then she does).