Yeah, thinning the glaze alone probably won't fix it. Glaze naturally pools in recesses because of surface tension, so even a thinner coat will collect in those deep fossil lines. What works better is thinning it AND wiping back with a damp sponge while it's still wet, right after you brush it on. Go over the whole surface lightly and you'll pull glaze off the high points and out of the crevices, leaving just a thin tint in the lines instead of a puddle. That way the bones read as texture instead of dark blobs. If you're using a glaze that breaks over texture, like many rust or speckled ones do, even a light coat will show the detail nicely because it thins itself on the edges. Your instinct about generous brushing was understandable though. Bare spots are worse than heavy glaze on a textured piece, so a lot of us learn this exact lesson. One pass, then sponge back, then maybe one more light coat only where it looks dry.
For the grabby roller thing, a few tricks. First, don't roll at full thickness. Let the slab firm up a bit, leather hard or close to it, so it resists dragging instead of smearing. Second, use a rolling guide or two paint sticks on either side so the roller can't wander and dig at the edges. Third, roll in one long pass with even pressure rather than going back and forth, and cover the roller with a sheet of canvas or a piece of muslin. The fabric keeps it from sticking and gives you a softer, cleaner impression.
Also, roll before you cut out the dish shapes. If you texture a big slab first and then cut your circles out of it, you never have to worry about distortion at the rim because you're not rolling anywhere near the finished edge. For the pooled ones you already fired, not much to do besides sanding the edges of the blob off and refiring, which rarely looks great. I'd just count those as the learning batch.