First of all, let's be clear: Two observations don't make a pattern.
Then again, I prefer the "evidence-based" route...
Your clues are not enough. If you want to go forward, you have to know where you are starting at. You need the "medical history" of a team/organization/case that you deem as "pathological", in order to be able to find out the whys, before you can go on with improvements.
Any enterprise/company/business that has not yet gone down is based on something that keeps running and, after a point, some balance typically strikes and almost all levels of management have formed a fair idea of the resources-to-needs ratio, as well as the cost-to-benefit ratio margins necessary to keep the company up and running. These are somewhat magic. These inexperienced developers are not being "done a favor" working in these projects. Generally, someone, somewhere, at some point, considered those developers fit for the purpose. Which brings us to the ...purpose!
Low productivity? Missed deadlines? It doesn't matter, as long as the company is up and running. Inexperienced developers cost less, which may be OK if you just need them to produce spreadsheets with formulas, spitting out some VBA scripts, a simple front-end for an in-house database, or other programming errands. There are probably companies that run exclusively on interns as IT support for years on end.
There is one thing you must never forget. Much as we may (occasionally) underestimate the technical knowledge of "Management" with respect to software development, there is something that they (and anyone, really) can tell you right off the tip of their head with respect to any system in the world, that is when they depend on it, of course.
Or it doesn't, which is when you have a problem and you call Houston asap. Management generally messes up when there is a problem. When there appears to be no problem at all, Management generally excels at rigidity. People that run the business want nothing changed because change involves risks. That is a primary element of mentality when money is involved and, fool yourself not, it is very effective. This mentality has kept businesses running safe since ...the beginning of civilization... and a day.
Regardless of whether you agree or disagree, I propose to keep the take-home message:
Up above, looking "downwards", there appears to be no problem at all.
If they are up and running and nobody is complaining that much, then that's that. Had anything been perceived as a problem to the well-being of the business, someone would have made a fuss about it long before your presence and you can be certain about this (citation needed alert, of course, anyone more experienced will definitely know better).
I understand I may have exaggerated a bit in my aforementioned commentary. However, I am simply trying to make a point. Take a step back. All your observations are pointless and mean nothing, until you clarify the one thing that rules them all: What is the task at hand and why does each involved administrative task-force (management etc.) not see a problem in the overall result. Why is it that you have identified multiple problems, while people that depend on the output of this team don't? Decode what it is that they see, so you can know what they perceive as a problem. A backlog might mean nothing to a Bank, but a small calculation error, a wrong decimal, a mistaken rounding, may make all the difference in the world. And as long as nobody complains, everyone is happy. When people are happy, they do their best to change nothing. Find out what "happy" means to all involved, up the ladder.
In short, get all relevant perspectives and get them quantified. Otherwise, you will be trying to teach a dog how to fly and, what is worse, you will never even understand why the dog does not want or need to fly... it may well be because its nutritional choices on the ground are far more diverse and voluminous.
I know this is practically not-an-answer as far as your actual question is concerned but, given your experience and suggestions, you seem to already have many good ideas and the fact that you have been unsuccessful does not necessarily mean you are doing things the "wrong" way. Plus other answers have provided many great ideas as well.