Joint operations is fine, especially with the new upcoming supply stations. Also, this is the only doctrine where you can find lefh and the arty officer together, the coordinated barrage can make lefhs fire again, even during cooldown.
I dont see anything being fine with it, tbh. It always was pure nooby 3v3+ commander, because you realistically wont be able to utilize PaK43 and LeFH even in semi-competitive games. You simply will end up out of pop-cap.
Also I suggest not to overestimate repair station and its impact. Its a cool ability, but its not a selling point and its not soviet HQ. Its more of a boosted Windustry countepart.
And on I side note, while having leFH fire second time with officer is a cool thing, I would prefere playing with Storm, because this one is not only usefull in every single scenario imaginable, but also can self-hard counter any enemy howi with recon+stuka.
I'il take this any day over officer and repair station, especially considering there are better comms with them.
But even if its a personal taste (but still I see absolutely no reason to pick Joint over Storm), still if you compare both LeFH commanders to both ML-20 commanders, Joint is complete lacklaster in terms of its over-all value and impact on the core army.
In fact, Storm is such a sexy doc after all the changes, I dont even know how second LeFH commander should look to be a even remotely competitive with it.