I realize this is stuff that has been in the game for 20 years so probably not first on the list for reprogamming.
However, the conversion efficiency of unmined rock to boulders and the way that efficiency interacts with miner skill has been tweaked a number of times since 2006, so it's not as if mining mechanics are off the table for possible improvement.
The observation I want to make is that the process of mining doesn't usually create a bunch of large boulders that can be carved into nice stone blocks. It usually makes a lot of rubble. The better you are at mining, the faster you can remove chunks of ore or coal from the rock, but you aren't trying to get big nice pieces of stone for masonry.
On the other hand, if you want a really nice piece of stone in the real world, the best way to get it is to cut it directly from a quarry rather than to shape a boulder into a slab or whatever.
I think it would be cool to allow quarrying to be designated separately from mining, and for quarrying to directly create blocks rather than chunks or boulders. Quarrying would always be slower than mining, but an expert quarrydwarf would leave behind a block close to 100% of the time. Most mason tasks would require blocks rather than boulders.