I mostly use fineliners too.
Even when I draw models posing "live" (actually on Zoom, most of the time) I do the preliminary sketches with thin, light gray pens, and then when I have the proportions mostly right (or at right as I can) I go in with a dark pen.
How long does a fineliner typically last? During the pandemic I tried doing Draw A Box, which demands fineliners. It seemed like they’d die on me extremely fast, and was a big reason I stopped. I don’t know if I got a bad batch or that’s just how they are.
My main problems with fineliners is not their "autonomy" but their durability.
I work on small scale drawings most of the time (A5) and I use small size tips.
I surely throw away more pens due a damaged tip than due to ink.
I am also using Japanese roller pens in very small sizes and these are sturdier, and last "long enough", in my experience
This could have been the issue. Maybe there was still ink in it, but the tip couldn’t deliver it.
I always had a bad time with them as a kid and ignored them for a couple decades. I only tried again after they were so highly recommended for this program. They wouldn’t accept work for review without using them. But they were exactly as I remembered, if not worse.
It’s possible I got unlucky at the start, but with it confirming my past memories, I was that interested in investing further in a program that required I use my least favorite implement.
Example: (NSFW) https://www.instagram.com/p/C_C5VQZOYVF/?img_index=8