It really depends on several factors. BCNMs can be very profitable, netting several hundred thousands of gil for a run, or they can reward relatively small, such as 20,000 gil. It really depends which BCNM you do, whether you succeed or not, and how lucky you get.
HNM can drop items worth millions of gil (a venemous claw would be one example, currently worth around 6,000,000 gil), or they can drop nothing of large value. If items are sold, it generally won't result in instantly making every rich, since the relatively large amount of gil must be split between many people.
Even if a very valuable item drops, most HNM linkshells won't simply sell the item and distribute all the gil, at least initially. Most HNM linkshells are more interested in growing as a group instead of gaining individual wealth, which means that if the expensive item can be used by someone to make the linkshell stronger, the item will usually be rewarded to them to use on future hunts. Obviously the person that gets the item benefits, but everyone else indirectly benefits too because the person can use the new item to perform their job better.
Granted, several HNMs hunt to make money, but most of these are already well established with a strong member base full of members who already possess great gear. Most likely the only members these linkshells would be interested in are people who are personal friends or fill a particular job role they lack.
In short, HNM linkshells can be profitable, but they are usually more oriented toward long-term goals. If you want to gain individual wealth, you're probably better off doing BCNM runs, farming, crafting, or using some other self-reliant method to gain your riches.