If you halve the output products of the reactions (1 fine for 2 boulders, 2 normal for 2 boulders), would that put a dent in the exp? At least you took pottery off oven operating, even though stone crafting is over used as is. I would dare say pottery could stand it's own skill again, one that encompasses all things relating to clay (from glazing to molding to baking), now that the fancier base materials are back and the process is more complex. At the same time, you could change the brick oven to use the furnace operating skill so that the total number of skills remains the same.
A completely different issue that's problematic is trying to deal with the ore processor when there's serious mining still going on. If there's a pick to be had, a miner is going to ignore the ore processing jobs and start on mining whatever QF related masterpiece is currently being dug. So other than strictly limiting the number of picks active (never mind the migrants showing up with said tools) or byzantine burrowing (shudder), it's almost impossible to get anyone to process ore consistently. I know you intended ore processing to extend the shelf life of the miner skill, but while the the skill is useful, it's one of the most important to get done quickest. Should just give ore processor duties to the blacksmith, that way a relatively useless skill can find new life and not interfere other automatic skills like mining and masonry.
A not so serious idea just occurred to me thinking of kobolds and their funtime secret tunnels; how about a mining station workshop for retired miners
Have it like the fishing station in that it's a mix of lowish % many ore reactions for 'stuff' and a few specific reactions for things like gypsum and nickle bearing rock. As silly as it sounds, even a 3x3 embark provides effectively limitless rock, and even more on larger maps for those that can tolerate the lag. Combine that with the shops now able to provide limitless amounts of whatever sundries via selling renewable goods and then using the tavern to generate limitless gold and hell, it would lessen the impact of using effing 'dirt' for color bricks!