That's like telling every server to get IP maskers. The people that do have Dos ability, aren't going to kill every server.
First off, no, it isn't like that. I have no idea where you even came up with the comparison.
The people who have the ability to DoS a server will do so to literally any server they desire. This is basically completely random and unless you're friends with a massive troll you're at risk of getting your server attacked.
It is the hosts choice to make Dup Admin only or not.
Congratulations for stating the obvious. The average joe doesn't know whether or not to make it admin only. There is no manual of "How to keep your server safe."
here is always going to be some exploit that can break a server, let it be events or bricks or dos. Every server is vulnerable of "getting forgeted over equally" nomatter if duplicator is admin or not.
There's a lot wrong with this too. You're trying to justify giving malicious code to a likely malicious person by saying "There's something else out there anyway." Yeah, maybe there IS something else out there, something that literally nobody but 1 person knows about. Is that bad? Yes. Does that justify giving a malicious exploit to someone? Hell loving no, by giving it to him you've raised the probability more servers will be attacked and as far as I'm concerned, you're the one responsible.
If somebody goes to the extent of doing dup spam, they will go to the extent to try different ways to hurt the server.
-A completely pointless list-
You're right! But you see, that makes no difference. You're still responsible for any server attacks that happen as a result of it.