You operate on the assumption that anyone on FAF can move dev resources to other projects. The main person responsible for Java Client was going to work on it regardless of what anyone else said (people already told him it was dumb when he started) and he wasn't going to change that. The people that moved in to help him after were people that preferred java and have openly said that they refuse to work in python.
There is no "simply refactor and improve it bro." There was nothing prohibiting work on python. Python was not worked on because no one wanted to work on it. To the point we couldn't even find a dude to just maintain it and iron out basic bugs for like a period of 2 years. It broke because no one wants to bother with it.
Dev resources are only wasted if there was an opportunity cost to a decision. If there wasn't, then there was nothing to waste. In fact forcefully prohibiting a dude to do his own thing which may or may not turn into a good thing down the road is in itself a waste.
It was made unofficial because no one was working on it for 2 years. Making the face of your community something no one even wants to work on and has not worked on in forever is terrible practice. Most of the improvements to Java Client were only possible once you forced everyone to use it and actually explain what they saw as terrible. And guess what? A lot of those things got improved upon because there are devs that actually do things on the client.
I do agree on your UI/UX complaints about things like the vault, though.