I've had a job like this. IMO it's okay to stay in this type of job as long as you are able to use the spare time and energy for your personal life, side projects, personal or career growth, etc. If you are forced to sit in an office and look busy, find another job.
It's also important to leave before you turn into that person who does barely anything for 10 years and are then unemployable. Unless you are okay with that. But you are asking on HN, so I'm guessing you are not okay with it.
>My sense of purpose is slowly but surely going away as I spend my days doing things that could be done so much more efficiently but that no one wants to improve. I have not had a real challenge at work for quite a long time now.
To paraphrase something posted on HN "Find a way to wind your own gears." I had a job like yours and I grew increasingly frustrated with the lack of control and the number of people who actually made things worse in their effort to control things. This job came soon after a challenging/interesting but really bad job (crazy work hours, toxic boss).
I was ready to quit the new job, but I had some stuff going on in my personal life so I ended up finding a career coach to explore where I was, how I got there, and where I wanted to go. It helped me find ways to wind my own gears. Part of that was realizing how much of my own growth had some from my own initiative and learning, not only from my job. I had to find ways to be true to my values despite being in a job where I felt my values were violated in a regular basis.
For example, we had a project where we had to process a large quantity of data. What followed was 6+ months of meetings and nonsense as people chased after building a big data stack and trying to build something that could solve all the companies data problems (hint: After more than a year nothing useful was delivered, but the PowerPoints were amazing)
Partly though the project I thought about how the solution might run on my laptop and spent two weeks building it in Python. I never told anybody what I did. But I learned a lot(!!) more about handling large quantities of data that I ever would have trying to influence that nonsense big data project.
>I spend most of my days having to wait for other people/companies or procrastinating which drives me crazy.
I think the important thing is to find a way to not let it drive you crazy. Channel that frustration into something useful for yourself. Lots of people will say "You have an opportunity to improve things and show them how it's done." But sometimes doing that is useless and not worth the energy. It can be like trying to use logic to convince a toddler to change their mind - the stupid person in that situation is not the toddler!
Also, realize that the vast majority of jobs are dealing with politics, waiting for other people, etc. It's important to find a way to deal with that without driving yourself crazy.