This is def an interesting "webcomic theory" topic and something I've spent a bit of time wondering about as well. Generally from my observations, the length that a project is worth working on is kind of proportionate to your goals for the comic which... sounds obvious to write out but like in more detail:
If the comic is something that the creator is making because they're really in love with that particular story and aren't too concerned with how "successful" it is, it seems like it's okay to dedicate as much time as need be to the comic. This is the category that I see a lot of like casual and hobbyist creators falling into.
On the flip side, it seems like if the goal is to either advance your skills a lot through the craft or to try and build a substantial audience, trying a lot of ideas and/or working on some "shorter" comics can potentially be beneficial. Like, I rarely see comics with small-to-medium sub bases exploding to super large numbers after they've been running for a long time. It feels like you kind of either strike gold, or you don't, and while most comics will definitely grow over time it's like... if you're going for 6 months and hit 200 subscribers, for example, it seems unlikely at that point that suddenly you'll be shooting up to 2 or 10k afterwards unless you get some sort of substantial platform-based marketing push.
it's also like when a comic has been running for a long time it can be daunting for people to choose to get invested in it, but if it already has a ton of subs it's somehow more inviting (potentially). Like "All of these people chose to stick around so it must be worth it!"
And the last thing that I can think of off the top of my head is the "your old pages are (usually) always worse than your new pages" that lead people into the redo loop. If you're really invested in a single, super long story it can be tempting to go back and redo parts of it, or just stress out that "the beginning isn't good enough/ will turn away readers" especially if it's like 1-2+ years old compared to your new stuff. Starting new projects kind of gives you a "get out of jail free" card in that regard- like the first pages of your new project will likely be amazing compared to the first pages of that older one.
That appeal + freshness drawing in new readers, combined with some of your old readers project hopping with you, seems to be a way to potentially take steps in the right direction, growth-wise. If you finally hit something that "strikes gold" then you can continue to either take it and run with it, or perhaps think of a different comic that would be better suited to ride the momentum (or just keep doing short comics if that's your jam!)
Granted this is still just observation and speculation on my part, since I'm 3/4 through my first year and just about to wrap up my first short-ish comic xD I'll have to see how it goes with project 2 and beyond. But I've seen at least a few artists pull off this type of path pretty well (on tapas at least, I admittedly don't follow webtoons very closely) where as a lot of authors seem to either just commit to a single really long story and are met with varying results as far as views/subs/etc. go.
I wrote too much, I'll stop now 
