Use a lot of wedges, a lot, and take a powerful leaf blower with you and blow away as much dirt as possible before you start cutting. Or even a gas engine power washer and roll a water tank to the stump to feed it.
I cut stumps flush when I have to, and usually just use an axe and broom first on that last lower cut below my felling cut areas. I quick whack the bark off and expose clean wood, man that helps. I dont do a lot of big trees, but with a little pre cleaning and using wedges, it goes much easier. IF I had to do a lot for a job, every day every day, etc. I would use the additional power equipment I mentioned first, plus a lot of wedges.
As to an actual dedicated stump cutting saw, how about one of those you stand up and have both hands on handle bar saws? Husky makes a modern one, and the rooskies have one too. It pivots. Pretty snazzy looking. You are standing up, the saw is down there, you twist it into the cut.
Here is the husky version, model 365H, via husky /russia and google translate (click on "translating..." if it doesnt open correctly)
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