So, let's see.
- magic exist, but only usable by noble
- Consuming is a disease where you have something overflowing from within
- magic tool can absorp those overflowing things
- noble doesn't mind keeping those with Consuming as slaves even with their supposedly high maintenance cost
See, if you take everything but the first one, you can guess that the overflowing thing is either magic fuel, all-healing potion, or maybe some sort of packable curse.
But add the first point, and that makes the explanation that those overwhelming things being magic fuels all the more likely.
Then there's the accident of MC making Toronbe grows just by holding it, and said Toronbe doesn't even need to absorp and destroying the soil nutrient. Which eliminates the possibility of MC exuding some sort of curses.
And with how the magic tool just get destroyed, instead of being "full" so it can be used when returned to the noble, I guess the possibility of it being some sort of healing item also get crossed out.
And so, we can concludes that nobles in this story are, indeed, assholes.