Isn't there any legacy code that could stop you from introducing pointless stuff like ESS and/or MMJD?

The problems with this implementation basically boil down to two major issues:

1) Interceptors exist

Interceptors are currently bubble immune and cannot be locked before they warp off. They invalidate nearly any defense you'd put up to guard your ESS. A lot of the balance here assumes you can guard it, which isn't really the case. There's no real viable way to kill an interceptor before it gets there, and with the ability of the interceptor to steal, warp out, and warp back in in 40s to get its tags the inty is virtually unkillable. This may be more of an issue that giving bubble immunity to interceptors was simply a mistake, but it makes the intended balance here not work.

2) A massive inbalance in the risk/reward that makes it a bad bet

You're asking people to risk 15% of their income for a 5% boost. That's a bad bet, especially considering point 1: you can't really do anything to affect the odds. You're going to wind up in the red most of the time, and 5% is not enough for people to want to play this game. Plus, the fact you are dumb enough to deploy an ESS means you're suddenly going to get a lot more interceptors in your space and you will lose a lot more often: word will spread about the people dumb enough to drop ESS that you can steal from and interceptors will decend on your space, losing you the money you risked for the ess, and losing you the money you'd have made while you safe up because hostiles are in your ratting system.

im suggesting leave plenty of risk. the timer would be kept short enough to form a quick fleet, but if you are going into enemy space you should be bringing more than 1 or 2 interceptors. the attackers have the advantage of already being organized and having guys on. the defenders would have to respond rapidly to get their fleet into the fight. getting a fleet to a system 10 jumps out takes time. so they wont wait for huge numbers they will throw out a quick fleet. also, hitting groups in off timezones will have major advantages.

At one point, I might've agreed with you. But these days, the sheer amount of people ratting in carriers tells a weeee bit of a different story, I think.

Here's a quick update on the changes we've made to the ESS, based on testing and feedback. There is a dev blog coming out tomorrow detailing these (and other changes) to the deployables in 1.1, but here's a basic overview.