"ps i watched carefuly the private server scene for more then 14 years, so i kinda know what i m talking about and i have very little money to spare" < What did you watch? For watching private scene (as developer/server owner), you need to understand the servers builds, nothing more you should care about. I connect to private server and instantly know what 'pack' they are using, what are the issues, etc. I understand what is happening under the hood. I doubt you know the difference between List and Set. In 2023 the private server scene is not described by server packs(files), it's based on the marketing budget. You can sell 'Snickers' candy for a cake's price.
I was always unsure about L2jMobius builds, until I decided to give some interest for Essence version.
My story is that I've bought L2jMobius membership and later on became an Contributor. (Fell out of that roll, because had some IRL problems which did not allow me to dedicate time to L2 Development).
While working with L2jMobius I found new connections, which allowed me to develop 'my own' Essence build (I was developing for a person who is a client of L2jMobius and was developing for him a bit faster than I was submitting patches for Mobius itself, it was not based on money, I was receiving patch notes which were not available for public (developed privately) in exchange to work and deliver some new implementations/corrections faster for that person than for whole L2jMobius project, though I always shared later the work with Mobius). That allowed me to gain base of known sources of Essence which are not publicly available (again to mention, I did not exchange any SVN private repos, worked with person who already had access same as me).
So where I'm going with this story? You care about 'leaks' when you develop something for L2jMobius, not when you pay him money, get the files and do nothing. Why you're afraid of leaks? The leak happens once per 2 months maybe, the SVN commits are daily. Why I hated leaks? Because I've implemented something dedicated for L2jMobius private clients, not the leachers. While I did not have my own base - those leaks and my code put everyone in same position - having the same features, if you don't have marketing budget, than you want to sell project for players by giving them features(I know it might contradict with the first paragraph of mine, but w/e, who understands - understands). The model is correct for L2jMobius to share a public version, it will attract new clients if they like the public version.
Okay, now we covered 'your scene watching of private servers', 'L2jMobius leaks' it's time for why L2jMobius is the only way for small private server to use for example while building Essence based project:
1. L2jMobius has a lot of clients, instead of working on your own, you have maybe 50+ people committing changes.
2. Mobius reviews all commits, does some QA, refactors the code to fit whole code base formatting etc..
3. You can write a question as a dummy server creator and get the answer (I was shocked what questions Mobius subscribers community receives, though I see that they are patient ones, I could not answer any questions without asking myself WTF is wrong, the person can't set his IP to launch the server and he's thinking about launching project, though even these problems are solved by community)
4. Don't judge book by the cover - if you receive leak of public version and you can't find certain feature working, you can always ask Mobius to check if someone is working on that, maybe day after the leak the feature will be implemented. Best case scenario, if possible, become a subscriber, just to try it.
TL;DR: If you're amateur server owner, don't know any of coding = you should not care, maybe Mobius is not dominating in Interlude/H5, but you can check for other version. Everything will be solved for you.
If you're developer (working alone and want other people help) - take these sources, make your own base, work on your code yourself + take patch notes submitted by other people.