"Micro" just means small and is easy enough to define, although one of the first companies to use the term "micro-distillery" was Jim Beam, about 15 years ago, in a completely phony way (for a product called Jacob's Well bourbon), and they got me fired for calling them out on it.
Terms such as "craft" and "artisan" are a little trickier, and spurious trademark claims notwithstanding, they suggest that something special and individualistic is being done that makes the final product more desirable in some tangible way. It suggests that "something" is important and cannot be achieved on an industrial scale.
America's industrial whiskey-makers grind their own grains, do their own mashing and fermentation, employ the traditional sour mash process, distill the beer at a relatively low proof (70% ABV is about average) using a unique double-distillation process (one pass through a column still, followed by one pass through a pot still), and age it in new charred barrels for, in most cases, no less than four years and often much more.
Some, though not all, still make their own yeast.
Who, among micro-distilleries, is more "craft" or "artisan" than that? My question, and it's a sincere inquiry, is if you want to make whiskey, don't you need to top that and, if so, how?
To me, it comes down to the difference between a professional and a hobbyist. Nothing wrong with having a hobby, but I suspect most micro-distillers don't consider it a hobby, so how can it be wrong to bulk up on the professionalism with some standards?