New Class Idea

[Niwashi]

But... Botanists already use scythes.

They also use axes. Should Warriors be worried?
(Yeah, I know. A botanist's hatchet is quite a ways removed from a battle axe. I just thought it seemed funny.)

"Ma" in this context most certainly implies darkness in the sense of dark equating to evil/negative. The character for "ma" conveys a dark/evil spirit or force, often associated with curses in the way that a person or object can be beset or imbued with a dark spirit or force. It is not conceptually synonymous with magic as you state.

"Mahou" can be flavored good or evil because just like its closest English translation, magic or mystical/supernatural abilities, it is general and does not have an implied good/bad/light/dark affinity like "ma" does. Saying that it can easily be taken as "evil force" or "demon magic" is a big stretch.

"Ma" can in some cases involve an evil or negative connotation and in other cases not. This is because, although its closest English equivalent is usually considered to be "devil" or "demon", the spirits of Japanese folklore and legends don't match those of the west. While Japanese demons are frequently harmful, they aren't inherently evil in the way that the demons of western religions and folklore are. But as supernatural beings, they are inherently magical, which is why "mahou" a compound formed of "demon-act" simply means magic, with neither a good nor bad connotation to it. (If you want to indicate in Japanese a demon that's actively evil, you can specify that separately, like with "akuma" a compound of "evil-demon".)

It seems a bit inconsistent that you'd claim "ma" gives an evil/negative connotation when it's used as part of a word, and then point out yourself that "mahou", which itself starts with that same "ma", doesn't have any such connotation. It seems like a better fit to regard the "ma" in "makenshi" as having about the same connotation that it has in "mahou" in referring just to magical power.