As I said, the only converter of mine that seems to have a capacity problem is the Namiki, but for practical reasons I also almost always run carts in that pen anyway.
I don't need a project, and I'm not super interested in locking a pen into a single mode of operation. The beauty of most pens is that you can go with carts OR with a converter, depending on mood. (Obviously some, like Pelikans and TWSBI, are bottle-fill only, but you know that going in.)
Yeah, I don't do cartridges for the same reason as others: I change the ink often, and the selection with cartridges is almost non-existent (and much more expensive per ml).
For a lot of pens, there is no "locking". You just remove the cartridge/converter, and add silicone, and you're good to go. You can always revert back.
I ran carts only in my Vanishing Point(s) for years, but largely because it was easier for travel and I found the ink color and consistency very pleasant.
Once I stopped traveling so much I started using more bottled ink, which is fun, but then you get to a point where you have a mental matrix about which inks work best with which paper in which nibs…
Just to expand on the time before refills. Most converters are under 1 ml. Having, say, 3-4 ml in your pen means you fill it a lot less frequently.
The thing keeping me away from eyedropping my pen is the inevitable burps.