1) 1 second reaction delay is too low. 1 second is in most cases time that you even notice that somebody spawn few hexes near you.. and until you choose the adequate reaction (run, attack, ..) you are almost death.
2) I think that delay should be equal to time, that your build needs to full reload APs. it is cca 5 seconds. So you would have time to run away or to eliminate enemy.
3) Again, its purpose is to eliminate abuse of instakill ability of mercs spawned in the middle of enemy group at spawn points. Players deserves possibility to react (defense, run away). We dont use fast relogs, every death by this mutants means game over. In opposite to merc leaders, that use supermutants as an artilery.
4) But this would not solve situation, where enemies would spawn i.e. 10 mercs at one time, or few seconds after.. You would not have a time or would not have a knowledge of which merc was spawned first, so it would cause the same mess like now, but cost of mutants would be little higher. So again, NO ACTIVE APROACH, again passive releasing and forget like now.
5) So set the game mechanis to level, that YOU HAVE TO CARE about your mercs, mutants, if you want to fully maximize their combat ability. Check area first (by sneakers,...). Eliminate basic threat and after this, deploy your mutants. Or prepare your muties to battleground before fight. No insta teleports with deadly ability into the group of enemies. This have nothing to do with gamebalance.
6) Set the game mechanics, that mercs would have to fight IN CITIES, NOT IN SPAWN ZONES only.
Only our aversion to fast and dual logging does not lead to situation, where the combat is only about artilering enemy artilery...