Iceblossom

Pencil marks can indeed be very difficult to get out. I do recommend using pencil but only on the back side of fabric. I have vision issues and have a hard time seeing the lines especially on busy scrap projects. I will often draw my quilting designs on parchment paper and then quilt through them -- and even then you have to be aware that the pencil marks can transfer through onto white thread.

In your case of having a marked top that is not quilted down, I would consider it very flimsy. The only time I wash something like that is if something happened like the cat peed on it.

As you've found, the fabric erasers are limited value. Any pink or other pencil toppers are likely to cause more problems than they solve.

Part of the problem with pencil is that there are little tiny bits of matter/graphite as well as staining from coming into contact with it. You might see if brushing over the lines with a toothbrush helps at all pre-quilting, and then maybe go over the lines again after quilting with the toothbrush and a bit of baking soda and a drop of water (mild abrasive, break down the graphite). That should still be safe for use on textiles but you would want to wash the entire top again after that.

In my years of quilting I had some heartbreaking lessons learned... I have never had to make a mistake to keep me humble, I am all sorts of humble. One of the things I've learned is things change and sometimes we have to accept that what we had in our heads and what we have on our beds maybe aren't quite the same things... Some of our flaws do loom large but fade over time. Some of us (dratted pencil lines) remind us that sometimes our decisions follow us way longer than they need to.