There's really not a one size fits all answer for water changes. At my house (well water) I can do 95% water changes with no ill effects at all, so I'm free to do as large as I'm in the mood to, but for someone else it might stress their fish.
There are factors that can influence your results each way, so in a sense opposite camps (small vs. large, more frequent vs. less frequent) can be right in a particular set of circumstances that don't extrapolate to other circumstances. You can start with a general guideline, but it's best imo to tweak it to your tank and your circumstances. For example:
Keep a low ph, bare tank, high feed, high protein type of tank and, sure, you may need frequent water changes, perhaps daily, because that combination creates a tank with low biological activity and high nitrogen output.
Less than ideal tap water-- high nitrates, phosphates, metals, or other issues from the tap and you may want to do smallish but more frequent water changes to not unduly upset your tank chemistry with each water change.
Moderate and sensible feed, moderate to moderately high ph (roughly between 7 and 8, sweet spot in the mid to upper 7s), sand or gravel, some combination of plants or driftwood, leaves, rocks, etc, and/or plenty of filter media capacity, good oxygen, and you should have a biologically active tank that, if not overstocked and with good tap water, and once a week, larger changes are plenty.
Also, sevs don't need low hardness ime, not any I've kept. I've never had a problem with GH and KH in the low to mid teens, ph in the mid 7s, including a wild rotkiel I had that lived at least 14-15 years (based on how long I had it, plus, being full grown, its age was at least two when I got it). Also, I don't normally bring up food, and I use and like more than one type-- ime to some degree which one makes your fish look best can vary a bit with species-- but ime rotkeils love NLS, including Thera-A, and look really good on it-- just my experience.
