Note that I have 15 years of weight lifting experience; that is, over the course of the last 15 years, I've lifted weights the entire time without any significant pauses more than 2 weeks, and my answer here is based off of my own experience as well as any references.
In short, NO, pull-ups cannot replace biceps curls, but at least if you perform chin-ups you can get the motion to be a bit more similar to curls.
First off, the pull-up is an exercise that is traditionally used to target the back, and while the biceps may work, they are in more supportive role, rather than a primary role. However, you can also somewhat control this by emphasizing certain parts of the movement. Nevertheless, I would not say that pullups in any way are the best exercise for building the biceps muscle.
That being said, you stated you you are using a "fingers forward" grip. This is technically a pronated grip. If you flip your hands around so that your fingers are pointing towards you, you assume a supinated grip, and would be performing chin ups. This article explains the difference in more detail with illustrations as well, but it will generally allow you to work the biceps harder than a pullup.
Again, both of these exercises are still considered mainly back exercises, but it's possible for you to emphasize and isolate the biceps more when performing the chinup movement. For example, if you were to focus on strictly the arms, truncate the motion by not going down as deep, it will work the biceps much more. I actually do this in the gym today, and I experience a nice "burn" in my biceps when I do it.
I would state with certainty that performing only pullups in place of curls would result in less biceps muscle gains vs. performing either only curls or curls and pullups.
I cannot state definitively how performing only curls vs. only biceps-focused chinups would affect your biceps muscle gains or losses, as there has never been a time when I did only those exercises in isolation.