Now this is the real chonker.
You say it's an instant gratification button for people who die.
People usually die when rounds are being escalated and the people that usually die tend to be security officers.
It is very appropriate to call ERT in a round where security is majorly crippled/ completely disabled.
Meaning that the situation in which ERT is appropriate to be called, is exactly the kind of situation you hope to avoid.
This is a self-fulfilling prohecy, ERT is most appropriate to be called when people are dying by big numbers. Big number of people means big dangerous ERT full of people with revenge boners. Which means it becomes more and more of a snowball.
Giving admins the abillity to call ERT whenever appropriate would not stop people from becoming ERT during the times when ERT is appropriate, which is usually during the times when security lost which results in the instant gratification.
In essence ERT itself IS the win button. And it doesn't matter if an admin or a player can press it, due to the fact that when ERT is not appropriate to call, there are no ghosts anyways.
tl;dr ERT is way too good at their job and overequipped, severely limiting their equipment would help much more than actually the way they're called.