There is a 9 level gap in-between 90-99 and this is opinion based. Also, read my reply more closely I referred a skill that does not work in conjunction with others but solely itself.
Last time I checked, you don't lose money making double astrals or nature in Runescape either so.
Mathematically speaking, the money you would make doing grenwalls to 99 hunter from 90 is garbage compared to the amount of time you'd save if you did jadinkos and used the seeds to make potions to train other skills faster. Training skills faster = less time spent training, you can spend your leftover time making money and make more money. So in terms of efficiency, it's WAY better to do jadinkos. Also, double astrals/natures are terrible xp, might as well do runespan and save tons of time and then spend that time making money, you'd make a lot more and get 99 rc faster.
