Personally I’d say about 40 sessions is a very reasonable assumption. One year of weekly play should be an achievable goal.
And yes, the point about other systems is very true. I’ve played lots of games which have a tighter focus than DnD.
Its not only that but D&D style games tend to gate a lot of options behind level. Given they don't have the zero-to-hero bias, that's much less true for a lot of ones outside the class/level paradigm.
True. I can’t really see an open ended Cthulhu game. Your characters are going to come to a bad end. The only question is how bad and when.
Or an open ended Dread game would require a honking huge Jenga tower.![]()
It was late in my RPG career that i even started trying to tie up campaigns into a nice ending, inspired by how a friend did it. That was about 25 years ago. I'd say that most of my campaigns wrap up nicely in the last 20 years or so. But it is always hard work for me to keep the enthusiasm going with an old campaign close to finishing, there is always a new and shiny incoming.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.