I've worked with Moodle adding custom reports and features to it. The shop where I worked at was stuck at Moodle 2.x and couldn't upgrade because it was a clusterfuck of custom code mixed with outdated plugins.
I feel you.
It worked, but god damn; I literally quit that job because of the stress of working with Moodle day in day out.
It's extremely hard to break into because like healthcare these gigantic institutions where nobody can get fired made choices ten to twenty years ago that have now become "the way it's done" and they won't accept a better solution.
In fairness, my university changed systems every year or so while I was there. They all sucked, so sticking with your existing solution is possibly not the worst decision.
Blackboard is a known aggressor with its patent portfolio and cash. They will acquire and extinguish or just kill you with a patent lawsuit if you present a significant threat to their products.
Moodle was pretty ick to begin with, but you should've seen the state of one install I had to work on by the time I got to it.
I still have nightmares.