I personally think that MIN is valuable and FSH not so much. There are a few annoyingly expensive materials that require fishing (with the help of alchemy usually), but they're expensive because they're annoying to get. MIN plays much differently in that if you see yourself making a couple stacks of electrum ingots or something you can spend a half hour or so gathering all the necessary materials for that endeavor. If you need some shark oil...well hopefully the sun just set and you need to go mooch a bunch of fish and hope.

It mostly depends on the scale you are looking at. Do you want to make millions? Gathering would definitely be helpful. Do you want to make tens or hundreds of millions? Well, if you're crafting that much then gathering is likely not so necessary.

I gather almost everything myself, but my goal is mostly independence, not market dominance or vast unnecessary (to me) riches. I like to be able to make anything I might need and have enough gil for anything that might cost gil and be outside of what I can craft or gather (mostly just dark matter, gyshal greens, teleporting, and housing).