I completely disagree with that. A good ROM hacker shouldn't rely on tools. Sure, they're useful (and should be made the most of), but a good hacker will realise that tools are limited. It's possible to get just as good, or better, results without tools if you put in the work.
For example, I inserted all the D/P Pokemon data into FR without tools; if you learn how it works, you don't have to spend hours editing each Pokemon individually in a tool. Same for sprites; I also inserted all 493 Pokemon sprites (front and back) without IrfanView or UnLZ-GBA. If I'd used those, then it would have taken me days. But working on it myself, I did it in a couple of hours. So if you can't fnd a tool for what you need to do, don't try and make do; figure it out and make your own tool for it. That's how I made the features in RHXP; they're all things which haven't been done before, or were far too time-consuming with old tools.
And then there's ASM. It's not necessary, but it can really make your hack look and play more uniquely if you use it. I don't know any myself, but if I actually wanted to make a hack, then I would learn it.
Obviously, don't try and do everything manually; if a tool exists for what you're trying to do, make use of it. But there will be times when there is no tool for what you're trying to do.