First of all, you don't have to have a mod to know if someone is Xraying. Second of all, you're supposed to read the rules on the wiki. Here's my answers to your complaints:
1. I'm pretty sure that at spawn there are signs telling you to read the rules on the wiki.
2. No warning should be needed for Xraying. If you Xray, you obviously don't want to commit to the server.
3. Supermods are allowed to have Xray mod to see if others are using it.
4. Again, you don't need a mod to see when someone is Xraying. It's pretty obvious.

Sorry for the mini-modding, but I just thought I'd respond to this.

 

What pops up when you type /rules


Sign at spawn that clearly says to type /rules

You are allowed to use mods that don't assist you like xray does. I personally use CJB, which is the Fly mod that the server supports.

And to answer your 4th point, we have various ways of determining whether or not a user has an xray mod.

 

Xray modding is an offense that results in a permanent ban, 100% of the time.

 

If they use xray mod, we will eventually catch them and they will face the same permanent ban that all xray users receive.