This sounds like a great opportunity to level up and learn some rare lessons.
It's easy to see problems and its easy to complain about them - but even if you're right, there's a vast gulf between complaining and driving change. You may be discouraged because you're hitting resistance but that's the nature of these things - if the organization already was ripe for and acting to fix these things, there'd be no need for you to help make it happen.
That's the nature of the leadership challenge - how do you get people to change things when they currently don't want to or think they cannot?
You think you see the right path, awesome, let's assume that's true. But if you can't find a way to make things better, then aren't you saying exactly the same thing that others are saying - "we have to live with it?"
You may not be in for that kind of challenge, you may just want to write code in a well set up environment, in which case you should absolutely leave. But if you want a real challenge of actually driving change and impact, of leveling up your leadership and seniority, this sounds like a great opportunity. Some will see it that way, others never will.
If you do see the opportunity, then the next question is "how" - finding a way to figure that out is going to be an amazing learning experience regardless of success.